Influence of glycosylation on the drug binding of human serum albumin

Quantitative analysis of selective glycosylation of saccharides with aromatic amines

Glycosylation, a part of the Maillard reaction, occurs non-enzymatically in food and biological processes. The selectivity of N-glycosylation was analyzed based on the reactivity of monosaccharides with aromatic amines, including aromatic amino acids, and the degree of molecular interaction (MI) measured using liquid chromatography. Furthermore, the chemical structures of reaction products were determined using X-ray crystallography and/or NMR. The possible reaction products were estimated in silico using the optimized energy values of different conformations. The MI energy values of amino groups and saccharides were calculated using in silico analysis using a model phase. Saccharides having larger MI values easily produced stable crystals of N-glycosides. The reaction rate of glucose (an energy saccharide) was slow, and it easily produced the Amadori compounds. The study of the reactivity of aromatic amines with saccharides, the measurement of the retention of monosaccharides on amino phase in chromatography, and the synthesis of N-glycosides for the determination of their structures will provide useful information about selective glycosylation for the modification of drug candidates to improve their water solubility.

Intensification of serum albumin amyloidogenesis by a glycation-peroxidation loop (GPL)

The interaction of reducing sugars with proteins leads to the formation of advanced glycation end products (AGE) and reactive oxidative species (ROS). ROS peroxidise free or membrane included unsaturated fatty acids, leading to generate reactive aldehydes as advanced lipid peroxidation end products (ALE). Aldehydes from lipid peroxidation (LPO) react with proteins to cause alteration of protein structure to exacerbate complication of diseases. Here we studied serum albumin glycation in the presence and absence of liposomes as a bio-membrane model to investigate protein structural changes using various techniques including intrinsic and extrinsic fluorescence spectroscopies and electron microscopy analysis. Accordingly, serum albumin glycation and fibrillation were accelerated and intensified in the presence of liposomes through a hypothesized glycation-peroxidation loop (GPL). Together, our results shed light on the necessity of reconsidering diabetic protein glycation to make it close to physiological conditions mimicry, more importantly, proteins structural change due to diabetic glycation is intensified in the proximity of cell membranes which probably potentiates programmed cell death distinct from apoptosis.

Changes in the albumin glycation site, plasma pentosidine and esRAGE concentrations before and after intensive diabetic treatment in patients with abnormally high glycated albumin levels

Background We have reported that the blood glucose normalization treatment reduced the albumin glycation sites and the intensity of albumin AGE fluorescence in patients with abnormally high glycated albumin levels. To clarify the relationship between glycaemic control status and levels of glycated proteins and related markers, we studied the change of the markers of the DM patients with and without fatty liver, liver cirrhosis and dialysis before and after the intensive diabetic treatment. Methods Eight diabetic patients with abnormally high glycated albumin levels (no complications: 2, fatty liver: 3, liver cirrhosis: 2, dialysis: 1) were recruited. In the hypoglycaemic treatment for these patients, the HbA1c, glycated albumin, albumin AGE fluorescence, pentosidine, endogenous secretory receptors for AGE (esRAGE) and glycation sites of albumin were determined. Results Glycated albumin and HbA1c levels dropped after the treatment. Albumin glycation sites decreased in almost the same pattern, irrespective of the type of complications. The fluorescence intensity and pentosidine concentrations decreased significantly. However, post-treatment pentosidine concentrations were higher than the reference interval in all cases. Average esRAGE concentrations did not change and were lower than the reference interval. Conclusions Hypoglycaemic treatment reduced the glycated albumin levels, glycation sites of albumin and AGE concentrations but not esRAGE concentrations in diabetic patients with or without fatty liver, liver cirrhosis, and dialysis. Checking and maintaining low glycated albumin levels would prevent the formation of AGE and may be useful to prevent the onset or progression of diabetes complications.

Structural and functional integrity of human serum albumin: Analytical approaches and clinical relevance in patients with liver cirrhosis

Human serum albumin (HSA) is the most abundant circulating plasma protein. Besides a significant contribution to the osmotic pressure, it is also involved in the fine regulation of many other physiological processes, including the balance of the redox state, the inflammatory and/or immunological responses, and the pharmacokinetic and pharmacodynamics of many drugs. Growing evidence suggests that HSA undergoes structural and functional damage in diseases characterized by an enhanced systemic inflammatory response and oxidative stress, as it occurs in chronic liver disease. Based on their clinical relevance, this review provides a summary of the most common post-translational modifications affecting HSA structural integrity and functions and their clinical relevance in the field of liver disease. The review also provides a critical description of the analytical approaches employed for the investigation of conformational alterations and the identification/quantitation of specific post-translational modifications affecting HSA. Finally, the analytical methods available for the assessment of two of the most clinically relevant non-oncotic properties of HSA, namely the binding capacity and the antioxidant activity, are critically reviewed. Among the available techniques particular attention is given to those proposed for the in vitro and in vivo investigation of structurally modified albumin.

Study on the interactions of sulfonylurea antidiabetic drugs with normal and glycated human serum albumin by capillary electrophoresis-frontal analysis

Diabetes is one of the most widespread diseases characterized by a deficiency in the production of insulin or its ineffectiveness. As a result, the increased concentrations of glucose in the blood lead not only to damage to many of the body's systems but also cause the nonenzymatic glycation of plasma proteins affecting their drug binding. Since the binding ability influences its pharmacokinetics and pharmacodynamics, this is a very important issue in the development of new drugs and personalized medicine. In this study, capillary electrophoresis-frontal analysis was used to evaluate the affinities between human serum albumin or its glycated form and the first generation of sulfonylurea antidiabetics, since their inadequate concentration may induce hypoglycaemia or on the contrary hyperglycaemia. The binding constants decrease in the sequence acetohexamide > tolbutamide > chlorpropamide > carbutamide both for normal and glycated human serum albumins, with glycated giving lower values. These results provide a more quantitative picture of how these drugs bind with normal and modified human serum albumin and indicate capillary electrophoresis-frontal analysis to be another tool for examining the changes arising from modifications of albumin, or any other protein, with all its benefits like short analysis time, small sample requirement, and automation.

Non-enzymatic glycation mediated structure–function changes in proteins: case of serum albumin

Albumin, a major plasma protein with extraordinary ligand binding properties, transports various ligands ranging from drugs, hormones, fatty acids, and toxins to different tissues and organs in the body.

Glycated Serum Albumin and AGE Receptors

In vivo modification of proteins by molecules with reactive carbonyl groups leads to intermediate and advanced glycation end products (AGE). Glucose is a significant glycation reagent due to its high physiological concentration and poorly controlled diabetics show increased albumin glycation. Increased levels of glycated and AGE-modified albumin have been linked to diabetic complications, neurodegeneration, and vascular disease. This review discusses glycated albumin formation, structural consequences of albumin glycation on drug binding, removal of circulating AGE by several scavenger receptors, as well as AGE-induced proinflammatory signaling through activation of the receptor for AGE. Analytical methods for quantitative detection of protein glycation and AGE formation are compared. Finally, the use of glycated albumin as a novel clinical marker to monitor glycemic control is discussed and compared to glycated hemoglobin (HbA1c) as long-term indicator of glycemic status.

Analysis of drug-protein interactions by high-performance affinity chromatography: interactions of sulfonylurea drugs with normal and glycated human serum albumin

High-performance affinity chromatography (HPAC) is a type of liquid chromatography that has seen growing use as a tool for the study of drug-protein interactions. This report describes how HPAC can be used to provide information on the number of binding sites, equilibrium constants, and changes in binding that can occur during drug-protein interactions. This approach will be illustrated through recent data that have been obtained by HPAC for the binding of sulfonylurea drugs and other solutes to the protein human serum albumin (HSA), and especially to forms of this protein that have been modified by non-enzymatic glycation. The theory and use of both frontal analysis and zonal elution competition studies in such work will be discussed. Various practical aspects of these experiments will be presented, as well as factors to consider in the extension of these methods to other drugs and proteins or additional types of biological interactions.

The efficiency of compounds with α-amino-β-mercapto-ethane group in protection of human serum albumin carbonylation and cross-linking with methylglyoxal

Substances containing an α-amino-β-mercapto-ethane pharmacophore may be used as effective methylglyoxal scavengers and inhibitors of protein carbonylation and cross-linking.

Review: Glycation of human serum albumin

Glycation involves the non-enzymatic addition of reducing sugars and/or their reactive degradation products to amine groups on proteins. This process is promoted by the presence of elevated blood glucose concentrations in diabetes and occurs with various proteins that include human serum albumin (HSA). This review examines work that has been conducted in the study and analysis of glycated HSA. The general structure and properties of HSA are discussed, along with the reactions that can lead to modification of this protein during glycation. The use of glycated HSA as a short-to-intermediate term marker for glycemic control in diabetes is examined, and approaches that have been utilized for measuring glycated HSA are summarized. Structural studies of glycated HSA are reviewed, as acquired for both in vivo and in vitro glycated HSA, along with data that have been obtained on the rate and thermodynamics of HSA glycation. In addition, this review considers various studies that have investigated the effects of glycation on the binding of HSA with drugs, fatty acids and other solutes and the potential clinical significance of these effects.

Impaired drug-binding capacities of in vitro and in vivo glycated albumin

Albumin, the major circulating protein in blood, can undergo increased glycation in diabetes. One of the main properties of this plasma protein is its strong affinity to bind many therapeutic drugs, including warfarin and ketoprofen. In this study, we investigated whether or not there were any significant changes related to in vitro or in vivo glycation in the structural properties and the binding of human albumin to both therapeutic drugs. Structural parameters, including redox state and ketoamine contents of in vitro and in vivo glycated purified albumins, were investigated in parallel with their affinity for warfarin and ketoprofen. High-performance liquid chromatography was used to determine the free drug concentrations and dissociation constants according to the Scatchard method. An alternative method based on fluorescence spectroscopy was also used to assess drug-binding properties. Oxidation and glycation levels were found to be enhanced in albumin purified from diabetic patients or glycated with glucose or methylglyoxal, after determination of their ketoamine, free thiol, amino group and carbonyl contents. In parallel, significant impairments in the binding affinity of in vitro and in vivo glycated albumin, as indicated by the higher dissociation constant values and confirmed by higher free drug fractions, were observed. To a lesser extent, this alteration also significantly affected diabetic albumin affinity, indicated by a lower static quenching in fluorescence spectroscopy. This work provides useful information supporting in vivo diabetic albumin could be the best model of glycation for monitoring diabetic physiopathology and should be valuable to know if glycation of albumin could contribute to variability in drugs response during diabetes.

Structural and immunological characterization of Amadori-rich human serum albumin: role in diabetes mellitus

Proteins modifications in diabetes may lead to early glycation products (EGPs) as well as advanced glycation end products (AGEs). Whereas no extensive studies have been carried out to assess the role of EGPs in secondary complications of diabetes, numerous investigators have demonstrated the role of AGEs. Early glycation involves attachment of glucose on ε-NH2 of lysine residues of proteins leading to generation of the Amadori product (an early glycation species). This study reports the structural and immunological characterization of EGPs of HSA because we believe that during persistent hyperglycemia the HSA, one of the major blood proteins, can undergo fast glycation. Glucose mediated generation of EGPs of HSA was quantitated as Amadori products by NBT assay and authenticated by boronate affinity chromatography and LC/MS. Compared to native HSA changes in glycated-HSA were characterized by hyperchromicity, loss in fluorescence intensity and a new peak in the FTIR profile. Immunogenicity of native- and glycated-HSA was evaluated by inducing antibodies in rabbits. Results suggest generation of neo-epitopes on glycated-HSA rendering it highly immunogenic compared to native HSA. Quantization of EGPs of HSA by authentic antibodies against HSA-EGPs can be used as marker for early detection of the initiation/progression of secondary complications of diabetes.

Effect of nonenzymatic glycosylation on the magnetic resonance imaging (MRI) contrast agent binding to human serum albumin

Enhanced nonenzymatic glycosylation (NEG) of human serum albumin (HSA) is observed in diabetic patients. This modifies some of the physiological functions of HSA, as the binding of ligands. Some gadolinium complexes, commonly used as MRI contrast agents, have a high affinity for HSA, which enhances their efficacy. The aim of this study is to evaluate the possible influence of the NEG of HSA on its affinity for some gadolinium chelates.

The glycation of albumin: structural and functional impacts

Oxidative stress and protein modifications are frequently observed in numerous disease states. Glucose constitutes a vital nutrient necessary to cellular oxygen metabolism. However, hyperglycemia-associated damage is an important factor in diabetes disorders. Albumin, the major circulating protein in blood, can undergo increased glycation in diabetes. From recent studies, it has become evident that protein glycation has important implications for protein activity, unfolding, and degradation, as well as for cell functioning. After giving a brief overview of the key role of albumin in overall antioxidant defense, this review examines its role as a target of glycation reactions. A synthesis of state of the art methods for measuring and characterizing albumin glycation is detailed. In light of recent data, we then report the impact of glycation on the structure of albumin and its various activities, especially its antioxidant and binding capacities. The biological impact of glycated albumin on cell physiology is also discussed, specifically the role of the protein as a biological marker of diabetes.

Characterization of the binding of sulfonylurea drugs to HSA by high-performance affinity chromatography

Sulfonylurea drugs are often prescribed as a treatment for type II diabetes to help lower blood sugar levels by stimulating insulin secretion. These drugs are believed to primarily bind in blood to human serum albumin (HSA). This study used high-performance affinity chromatography (HPAC) to examine the binding of sulfonylureas to HSA. Frontal analysis with an immobilized HSA column was used to determine the association equilibrium constants (Ka) and number of binding sites on HSA for the sulfonylurea drugs acetohexamide and tolbutamide. The results from frontal analysis indicated HSA had a group of relatively high-affinity binding regions and weaker binding sites for each drug, with average Ka values of 1.3 (+/-0.2) x 10(5) and 3.5 (+/-3.0) x 10(2) M(-1) for acetohexamide and values of 8.7 (+/-0.6) x 10(4) and 8.1 (+/-1.7) x 10(3) M(-1) for tolbutamide. Zonal elution and competition studies with site-specific probes were used to further examine the relatively high-affinity interactions of these drugs by looking directly at the interactions that were occurring at Sudlow sites I and II of HSA (i.e., the major drug-binding sites on this protein). It was found that acetohexamide was able to bind at both Sudlow sites I and II, with Ka values of 1.3 (+/-0.1) x 10(5) and 4.3 (+/-0.3) x 10(4) M(-1), respectively, at 37 degrees C. Tolbutamide also appeared to interact with both Sudlow sites I and II, with Ka values of 5.5 (+/-0.2) x 10(4) and 5.3 (+/-0.2) x 10(4) M(-1), respectively. The results provide a more quantitative picture of how these drugs bind with HSA and illustrate how HPAC and related tools can be used to examine relatively complex drug-protein interactions.

Elucidation of the human serum albumin (HSA) binding site for the Cu-PTSM and Cu-ATSM radiopharmaceuticals

The Cu-PTSM (pyruvaldehyde bis(N(4)-methylthiosemicarbazonato)copper(II)) and Cu-ATSM (diacetyl bis(N(4)-methylthiosemicarbazonato)copper(II)) radiopharmaceuticals exhibit strong, species-dependent binding to human serum albumin (HSA), while Cu-ETS (ethylglyoxal bis(thiosemicarbazonato)copper(II)) appears to only exhibit nonspecific binding to human and animal serum albumins. This study examines the structural basis for HSA binding of Cu-PTSM and Cu-ATSM via competition with drugs having known albumin binding sites. Warfarin, furosemide, ibuprofen, phenylbutazone, benzylpenicillin, and cephmandole were added to HSA solutions at drug:HSA mole ratios from 0 to 8:1, followed by quantification of radiopharmaceutical binding to HSA by ultrafiltration. Warfarin, a site IIA drug, progressively displaced both [(64)Cu]Cu-PTSM and [(64)Cu]Cu-ATSM from HSA. At 8:1 warfarin:HSA mole ratios, free [(64)Cu]Cu-PTSM and [(64)Cu]Cu-ATSM levels increased 300-500%. This was in contrast to solutions containing ibuprofen, a site IIIA drug; no increase in free [(64)Cu]Cu-PTSM or [(64)Cu]Cu-ATSM was observed except at high ibuprofen:HSA ratios, where secondary ibuprofen binding to the IIA site may cause modest radiopharmaceutical displacement. By contrast, and consistent with earlier findings suggesting Cu-ETS exhibits only nonspecific associations, [(64)Cu]Cu-ETS binding to HSA was unaffected by the addition of drugs that bind in either site. We conclude that the species-dependence of Cu-PTSM and Cu-ATSM albumin binding arises from interaction(s) with the IIA site of HSA.

Physiological and pathological changes in the redox state of human serum albumin critically influence its binding properties

Binding and transport of a number of endogenous and exogenous compounds is an important function of the main plasma protein, albumin. In vivo and in vitro, albumin may be oxidatively modified in different ways with different agents at different sites. These modifications have various consequences on the physiological functions of albumin. Diabetes mellitus, liver diseases and nephropathy are just a few examples of disorders in which oxidative stress is involved and altered albumin functions have been described. This review is focussed on the consequences of oxidative modification on the binding properties of albumin. These range from no effect to decreased or increased binding affinities depending on the ligand under investigation and the type of modification. Indicators for modification include glycosylation, disulphide formation or the content of carbonyl groups. The redox state of albumin can affect the binding properties in several ways, including altered conformation and consequently altered affinities at binding sites and altered binding when the binding reaction itself is redox sensitive. The physiological or pathophysiological concentrations of different oxidatively modified albumin molecules vary over a wide range and are crucial in assessing the clinical relevance of altered ligand binding properties of a particularly modified albumin species in various disease conditions.

Structural and glycation site changes of albumin in diabetic patient with very high glycated albumin

BACKGROUND

Glycated albumin (GA) has been utilized to monitor mid-term glycemic control, and reflects the status of blood glucose more rapidly and effectively than hemoglobin A(1c) (HbA(1c)). To examine the relationship between GA level and structural changes or glycation sites of albumin, we analyzed pre- and post-treatment samples from a diabetic patient with extraordinary increase of GA.

METHOD

A female diabetic patient with poor glycemic control had a GA >94% and was treated with intensive insulin therapy to decrease blood glucose. We analyzed changes in fluorescence derived from tryptophan (Trp) and advanced glycation end product (AGE) of albumin isolated/purified from pre- and post-treatment samples. To determine the sites of glycation of albumin, samples were carboxymethylated and digested by Glu-C endoprotease, and peptides were analyzed using liquid chromatography/mass spectrometry.

RESULTS

GA level decreased almost linearly and reflected the improved glycemic state well. Trp-related fluorescence of pre- and post-treated samples did not change while AGE-related fluorescence increased depending on GA level. Ten major glycation sites were detected in the pre-treatment sample, while 3 major glycation sites were detected in post-treated samples.

CONCLUSIONS

GA level reflects the status of blood glucose more rapidly than HbA(1c). Since GA level was related to AGE-related fluorescence and number of glycation sites, it might be a good marker for not only glycemic control of diabetic patients but also structural and functional changes of albumin.

In silico ADME modelling 2: Computational models to predict human serum albumin binding affinity using ant colony systems

Modelling of in vitro human serum albumin (HSA) binding data of 94 diverse drugs and drug-like compounds is performed to develop global predictive models that are applicable to the whole medicinal chemistry space. For this aim, ant colony systems, a stochastic method along with multiple linear regression (MLR), is employed to exhaustively search and select multivariate linear equations, from a pool of 327 molecular descriptors. This methodology helped us to derive optimal quantitative structure-property relationship (QSPR) models based on five and six descriptors with excellent predictive power. The best five-descriptor model is based on Kier and Hall valence connectivity index--Order 5 (path), Auto-correlation descriptor (Broto-Moreau) weighted by atomic masses--Order 4, Auto-correlation descriptor (Broto-Moreau) weighted by atomic polarizabilities--Order 5, AlogP98, SklogS (calculated buffer water solubility) [R=0.8942, Q=0.86790, F=62.24 and SE=0.2626]; the best six-variable model is based on Kier and Hall valence connectivity index of Order 3 (cluster), Auto-correlation descriptor (Broto-Moreau) weighted by atomic masses--Order 4, Auto-correlation descriptor (Broto-Moreau) weighted by atomic polarizabilities--Order 5, Atomic-Level-Based AI topological descriptors--AIdsCH, AlogP98, SklogS (calculated buffer water solubility) [R=0.9128, Q=0.89220, F=64.09 and SE=0.2411]. From the analysis of the physical meaning of the selected descriptors, it is inferred that the binding affinity of small organic compounds to human serum albumin is principally dependent on the following fundamental properties: (1) hydrophobic interactions, (2) solubility, (3) size and (4) shape. Finally, as the models reported herein are based on computed properties, they appear to be a valuable tool in virtual screening, where selection and prioritisation of candidates is required.

Macromolecule-ligand binding studied by the Hummel and Dreyer method: current state of the methodology

The use of the Hummel and Dreyer method to measure binding parameters of ligand-macromolecule associations is reviewed. The possibility to determine the number of binding sites and their association constants, even in the case of low affinity, and to control the free ligand concentration as an independent variable are the main advantages of the method. The conditions of the validity are rapid equilibrium kinetics, independence between ligand binding and macromolecule association, and identical retention rates between free and bound macromolecules. Initially developed on soft gels, the method has been applied to high-performance chromatography and capillary zone electrophoresis. Technical progress such as increase in resolution, detection sensitivity, and automation have improved its utilization. The binding parameters given by the Hummel and Dreyer method are in general similar to those obtained by other techniques, in comparable experimental conditions (equilibrium dialysis, ultrafiltration, frontal elution, vacancy peak method, vacancy affinity capillary electrophoresis, retention analysis, affinity chromatography and affinity capillary electrophoresis, physical methods). The choice between these methods is directed by material availability and practical constraints. Separation by new types of chromatographic columns or by capillary zone electrophoresis would enable the study of the simultaneous binding of different drugs on the same macromolecule and their competition.

Predicting plasma protein binding of drugs: a new approach

In spite of the large amount of plasma protein binding data for drugs, it is not obvious and there is no clear consensus among different disciplines how to deal with this parameter in multidimensional lead optimization strategies. In this work, we have made a comprehensive study on the importance of plasma protein binding and the influencing factors in order to get new insights for this molecular property. Our analysis of the distribution of percentage plasma protein binding among therapeutic drugs showed that no general rules for protein binding can be derived, except for the class of chemotherapeutics, where a clear trend towards lower binding could be observed. For the majority of indication areas, however, empirical rules are missing. We present here an extensive list of multiply determined primary association constants for binding to human serum albumin (HSA) for 138 compounds from the literature. Correlating these binding constants with the percentage fraction of protein bound showed that the percentage data above 90%, corresponding to a binding constant below 6 microM, are of insufficient accuracy. Furthermore, it could be demonstrated that the lipophilicity of drugs, traditionally felt to dominate binding to HSA, is not the only relevant descriptor. Here, we report a generic model for the prediction of drug association constants to HSA, which uses a pharmacophoric similarity concept and partial least square analysis (PLS) to construct a quantitative structure-activity relationship. It is able to single out the submicromolar to nanomolar binders, i.e. to differentiate between 99.0 and 99.99% plasma protein binding. Depending on the system, this can be important in medicinal chemistry programs and may together with other computed physicochemical and ADME properties assist in the prioritization of synthetic strategies.

Interaction of ochratoxin A with human serum albumin. Binding sites localized by competitive interactions with the native protein and its recombinant fragments

Competitive interactions of ochratoxin A (OTA) and several other acidic compounds were utilized to gain insight into the localization of binding sites and the nature of binding interactions between anionic species and human serum albumin (HSA). Depolarization of OTA fluorescence in the presence of a competing anion was used to quantify ligand-protein interactions. The results obtained were rationalized in terms of OTA displacement from its major binding site. Based on their ability to displace OTA, two distinct groups of the anionic ligands were revealed. The first group contained structurally diverse compounds that shared a common binding site in subdomain IIA (Sudlow Site I). The second group consisted of three non-steroidal anti-inflammatory drugs, which showed much lower affinity to Site I than the OTA dianion. The major site for these drugs was located in domain III. Fluorescence spectroscopy measurements of OTA, warfarin (WAR) and naproxen (NAP) complexes with recombinant proteins corresponding to the domains of HSA (D1-D3) revealed binding to all domains but with different affinities. The binding constants for OTA and WAR decreased in the series D2z.Gt;D3>D1. In contrast, NAP showed the most favorable interaction with D3 and comparable affinities to the two remaining domains. The OTA binding constant for D2, 7.9 x 10(5) M(-1), was smaller than the largest constant for HSA by a factor of approximately 7. The binding constant for OTA with D3, 1.1 x 10(5) M(-1), was very close to that of the secondary binding site for HSA.

Cheminformatic models to predict binding affinities to human serum albumin

Models to predict binding affinities to human serum albumin (HSA) should be very useful in the pharmaceutical industry to speed up the design of new compounds, especially as far as pharmacokinetics is concerned. We have experimentally determined through high-performance affinity chromatography the binding affinities to HSA of 95 diverse drugs and druglike compounds. These data have allowed us the derivation of quantitative structure-activity relationship models to predict binding affinities to HSA of new compounds on the basis of their structure. Simple linear, one-variable models have been derived for specific families of compounds (r(2) > or = 0.80; q(2) > or = 0.62): beta-adrenergic antagonists, steroids, COX inhibitors, and tricyclic antidepressants. Also, global models have been derived to be applicable to the whole medicinal chemical space by using the full database of HSA binding constants described above. For this aim, a genetic algorithm has been used to exhaustively search and select for multivariate and nonlinear equations, starting from a large pool of molecular descriptors. The resulting models display good fits to the experimental data (r(2) > or = 0.78; LOF < or = 0.12). In addition, both internal (cross validation and randomization) and external validation tests have demonstrated that these models have good predictive power (q(2) > or = 0.73; PRESS/SSY < or = 0.23; r(2) > or = 0.82 for the external set). Statistical analysis of the equation populations indicates that hydrophobicity (as measured by the ClogP) is the most important variable determining the binding extent to HSA. In addition, structural factors (especially the topological (6)chi(ring) index and some Jurs descriptors) also frequently appear as descriptors in the best equations. Therefore, binding to HSA turns out to be determined by a combination of hydrophobic forces together with some modulating shape factors. This agrees with X-ray structures of HSA alone or bound to ligands, where the binding pockets of both sites I and II are composed mainly of hydrophobic residues.

Fluorometric and mass spectrometric analysis of nonenzymatic glycosylated albumin

Albumin is the major transport protein in blood and intramolecular movement contributes to this function. Nonenzymatic glycosylation (NEG) of albumin occurs in diabetes and, in this study, fluorometric methods were used to determine the effect of increasing levels of NEG upon intramolecular movement in human serum albumin. Low levels of NEG significantly reduced and left-shifted Trp fluorescence, reduced quenching by acrylamide and inhibited penetration of bis-ANS, while these changes became only modestly more pronounced at higher levels of NEG. Mass spectrometry of tryptic and CNBr NEG-HSA fragments identified potential glycosylation sites and demonstrated only late glycosylation of the C- and N-terminal regions of the protein. Similar changes in diabetes may contribute to altered transport function in these patients.

Binding properties of human albumin modified by covalent binding of penicillin

Derivatisation of lysine residues in human albumin was performed in vitro by reaction with penicillin G. This modification reaction has been reported to occur in patients treated with high dosages of the antibiotic. The structure of the modified protein was characterised by mass spectrometry and circular dichroism. The number of the lysine residues involved depends on the time of incubation and on the drug/protein molar ratio. The secondary structure of the modified protein does not change significantly with respect to the native protein. Furthermore, the binding properties of the modified albumin were characterised by CD spectroscopy. Phenylbutazone, diazepam and bilirubin, known to bind to specific binding areas, were used as markers. A decrease of the affinity to the high-affinity binding sites was observed after the modification.