Use of transgenic mice for the characterization of human alpha 1-acid glycoprotein (orosomucoid) variants

Hydrolase Activity of the Genetic Variants of Human Alpha-1-Acid Glycoprotein

In human plasma, the main agent of hydrolysis of the ester-type prodrug of levodopa, designated ONO-2160, is alpha-1-acid glycoprotein (AGP), which is a mixture of the F1*S and A variants at molar ratios of 3:1 to 2:1. In this study, the mechanism of AGP esterase-like activity was investigated by evaluating the contribution of the F1*S and A variants to ONO-2160 hydrolysis and identifying the AGP hydrolase active site. We found that although both variants hydrolyzed ONO-2160, their hydrolase activities were different. The intrinsic plasma clearance of the F1*S variant (0.441 mL/h/mg protein) was approximately 30 times higher than that of the A variant (0.0148 mL/h/mg protein), indicating that the F1*S variant contributed the most to AGP esterase-like activity. To identify the hydrolase active site of AGP, we performed inhibition studies of ONO-2160 hydrolysis using 12 AGP-binding drugs with various ligand-binding constants and binding selectivities to the two AGP variants. Inhibition of activity was positively correlated with the constant of ligand binding to the F1*S variant. In addition, compounds with high affinity to the F1*S variant inhibited ONO-2160 hydrolysis the most. Together, our data indicate that ONO-2160 is predominantly hydrolyzed by the F1*S variant at its ligand-binding site.

Implications of plasma protein binding for pharmacokinetics and pharmacodynamics of the γ-secretase inhibitor RO4929097

PURPOSE

Understanding of plasma protein binding will provide mechanistic insights into drug interactions or unusual pharmacokinetic properties. This study investigated RO4929097 binding in plasma and its implications for the pharmacokinetics and pharmacodynamics of this compound.

EXPERIMENTAL DESIGN

RO4929097 binding to plasma proteins was determined using a validated equilibrium dialysis method. Pharmacokinetics of total and unbound RO4929097 was evaluated in eight patients with breast cancer receiving RO4929097 alone and in combination with the Hedgehog inhibitor GDC-0449. The impact of protein binding on RO4929097 pharmacodynamics was assessed using an in vitro Notch cellular assay.

RESULTS

RO4929097 was extensively bound in human plasma, with the total binding constant of 1.0 × 10(6) and 1.8 × 10(4) L/mol for α1-acid glycoprotein (AAG) and albumin, respectively. GDC-0449 competitively inhibited RO4929097 binding to AAG. In patients, RO4929097 fraction unbound (Fu) exhibited large intra- and interindividual variability; GDC-0449 increased RO4929097 Fu by an average of 3.7-fold. Concomitant GDC-0449 significantly decreased total (but not unbound) RO4929097 exposure. RO4929097 Fu was strongly correlated with the total drug exposure. Binding to AAG abrogated RO4929097 in vitro Notch-inhibitory activity.

CONCLUSIONS

RO4929097 is highly bound in human plasma with high affinity to AAG. Changes in plasma protein binding caused by concomitant drug (e.g., GDC-0449) or disease states (e.g., ↑AAG level in cancer) can alter total (but not unbound) RO4929097 exposure. Unbound RO4929097 is pharmacologically active. Monitoring of unbound RO4929097 plasma concentration is recommended to avoid misleading conclusions on the basis of the total drug levels.

A site-directed mutagenesis study of drug-binding selectivity in genetic variants of human alpha(1)-acid glycoprotein

Human alpha(1)-acid glycoprotein (AGP), a major carrier of many basic drugs in circulation, consists of at least two genetic variants, namely A and F1*S variant. Interestingly, the variants of AGP have different drug-binding properties. The purpose of this study was to identify the amino acid residues that are responsible for the selectivity of drug binding to genetic variants of AGP using site-directed mutagenesis. First, we screened amino acid residues in the region proximal to position 100 that are involved in binding of warfarin and dipyridamole, which are F1*S-specific ligands, and of propafenone, which is an A-specific ligand, using ultrafiltration. In the F1*S variant, His97, His100, and Trp122 were involved in either warfarin- or dipyridamole-binding, while Glu92, His100, and Trp122 participated in the binding of propafenone in the A variant. Exchange of the residue at position 92 between AGP variants reversed the relative strength of propafenone binding to the two variants, but had a markedly different effect on binding of warfarin and dipyridamole. These findings indicate that the amino acid residue at position 92 plays a significant role in drug-binding selectivity in AGP variants, especially for drugs that preferentially bind to the A variant.

Biliverdin is the endogenous ligand of human serum alpha1-acid glycoprotein

alpha(1)-Acid glycoprotein (AAG), an acute phase component of the human serum, is a prominent member of the lipocalin family of proteins showing inflammatory/immunomodulatory activities and promiscuous drug binding properties. Both three-dimensional structure of AAG and its precise biological function are still unknown and only a few endogenous AAG ligands have been described to date. CD spectroscopic studies performed with commercial AAG and the separated genetic variants revealed high-affinity binding of biliverdin (BV) and biliverdin dimethyl ester to the 'F1/S' fraction of the protein. The preferential accommodation of the right-handed, P-helicity conformers of the pigments by the protein matrix resulted in strong induced CD activity, which was utilized for estimation of the binding parameters and to locate the binding site. It was concluded that both pigments are bound in the central beta-barrel cavity of AAG, held principally by hydrophobic interactions. Possible biological implications of the BV binding ability of AAG with special emphasis on the heme oxygenase-1 pathway are discussed.

Biantennary Glycans as Well as Genetic Variants of α1-Acid Glycoprotein Control the Enantioselectivity and Binding Affinity of Oxybutynin

PURPOSE

The purpose of this study was to investigate the role of biantennary branching glycans of alpha1-acid glycoprotein (AGP) and its genetic variants in the enantioselective binding of oxybutynin (OXY).

METHOD

Human native AGP was separated using imminodiacetate-copper (II) affinity chromatography into two fractions, the A variant and a mixture of the F1 and S variants (F1-S). These fractionated AGPs were further separated by concanavalin A affinity chromatography into two fractions, with and without biantenarry glycans. An on-line high-performance liquid chromatography (HPLC) system consisting of a high-performance frontal analysis column, an extraction column, and an analytical HPLC column was developed to determine the binding affinities of OXY enantiomers for respective AGP species.

RESULTS

The total binding affinity as well as the enantiomeric selectivity of OXY in the F1-S mixed variant was significantly higher than that for the A variant, indicating that the chiral recognition ability of native AGP for the OXY enantiomers highly depends on the F1-S mixed variant. Furthermore, not only the genetic variants but also bianntenary glycans of AGP affect the binding affinity of OXY and are also responsible for the enantioselectivity.

CONCLUSIONS

Both genetic variants and glycan structures significantly contribute to the enantioselectivity and the binding affinity of OXY.

Glycosylation study of the major genetic variants of human alpha1-acid glycoprotein and of their pharmacokinetics in the rat

Human alpha1-acid glycoprotein (AAG) is a mixture of at least two genetic variants, the A variant and the F1 and/or S variant or variants, which are encoded by two different genes. AAG is also an extensively glycosylated protein which possesses five N-linked glycans exhibiting substantial heterogeneity in their structures. The first objective of this study was to investigate the glycosylation of the two major gene products of AAG, i.e. the A variant and a mixture of the F1 and S variants (F1*S). To this end, we combined a chromatographic method for the fractionation of the AAG variants with a lectin-binding assay to characterise the glycosylation of purified glycoproteins. Secondly, because the oligosaccharides can influence the disposition of AAG, a kinetic study of the AAG variants was carried out in the rat. After intravenous administration of whole human AAG, the separation and quantification of the AAG variants in plasma was performed by application of specific methods by isoelectric focusing and immunonephelometry. The binding studies carried out on a panel of lectins showed significant differences in the lectin-binding characteristics of the separated F1*S and A variants, accounting for differences in the degree of branching of their glycan chains and substitution with sialic acid and fucose. The plasma concentration-time profiles of the F1*S and A variants were biphasic, and only small differences were observed between the variants for their initial and terminal half-lives, clearance and distribution volume. This indicates that the structural differences between the two AAG gene products do not affect their pharmacokinetics in the rat. Specific drug transport roles have been previously demonstrated for the F1*S and A variants, calling for further investigations into their effects on the disposition of drugs they bind in plasma. The present study shows that such investigations are possible without being complicated by kinetic differences between these variants.

Specific ligand binding on genetic variants of human α1-acid glycoprotein studied by circular dichroism spectroscopy

Human alpha1-acid glycoprotein displays genetic polymorphism. Different drug binding properties of the two main genetic products (F1-S and A variants) have been demonstrated. In search for specific circular dichroism (CD) probes, dicumarol and acridine orange were found to specifically bind to the F1-S and A variants, respectively. Dicumarol binding to the F1-S variant produced induced Cotton effects originating from the favored chiral conformation of the bound label. Acridine orange gave induced biphasic Cotton effects due to chiral intermolecular exciton interaction between label molecules bound to the A variant. Displacement of the CD probes by specific marker ligands was demonstrated. The induced CD spectrum of dicumarol was found to change sign in the presence of imipramine, as a manifestation of high-affinity ternary complex formation on the F1-S variant.

Differential binding of disopyramide and warfarin enantiomers to human alpha(1)-acid glycoprotein variants

AIMS

The F1S and A genetic variants of alpha1-acid glycoprotein (AAG) change under various physiological and pathological conditions. They also vary in their drug binding abilities. We have studied the stereoselective binding ability of each of the AAG variants using enantiomers of disopyramide (DP) and warfarin (WR).

METHODS

The AAG variants were separated by hydroxyapatite chromatography. Binding of drug enantiomers to the AAG variants was studied by the Hummel-Dreyer method. The characteristics of the binding activities were examined by Scatchard plot analysis. The first five amino-terminal amino acids (residues 112-116) of the cyanogen bromide (CNBr) fragment (residues 112-181) of each of the separated AAG fractions were elucidated by Edman degradation.

RESULTS

Commercial AAG was separated into two main fractions. Residues 112-116 of fraction 2 were identical to the amino acid sequences predicted from the AAG A gene, LAFDV, and encode the F1S variant. In fraction 3, the deduced amino acid sequence of the AAG B gene, FGSYL, was established, and encodes the A variant. The binding affinities of both DP enantiomers in fraction 3 were significantly higher than those in fraction 2. The differences between dissociation constants (Kd) in fractions 2 and 3 were 5.2-fold for (S)-DP (P < 0.05) and 3.7-fold for (R)-DP (P < 0.001). The dissociation constant of (S)-DP (0.39 +/- 0.08 micro m) was lower than that of (R)-DP (0.53 +/- 0.10 micro m) in fraction 3 [95% confidence interval (CI) - 0.282, - 0.010; P < 0.05], although the binding activities of the DP enantiomers were almost the same in fraction 2. By contrast WR enantiomers had a higher binding affinity in fraction 2 than in fraction 3, the differences in dissociation constants between fractions 2 and 3 being 12.6-fold for (S)-WR (P < 0.001) and 8.3-fold for (R)-WR (P < 0.001). The dissociation constant of (S)-WR (0.28 +/- 0.10 microm) was significantly lower than that of (R)-WR (0.48 +/- 0.08 microm) in fraction 2 (95% CI - 0.369, - 0.028; P < 0.05), but there were no significant differences between the binding activities of WR enantiomers in fraction 3.

CONCLUSIONS

DP and WR enantiomers bind preferentially to fraction 3 and fraction 2, respectively. Fractions 2 and 3 are encoded by the AAG A and the AAG B genes, respectively.

Capillary electrophoretic study on pH dependence of enantioselective disopyramide binding to genetic variants of human alpha1-acid glycoprotein

A high-performance frontal analysis-capillary electrophoresis (HPFA-CE) method was applied to investigate the effect of pH on the drug binding properties of genetic variants of human alpha1-acid glycoprotein (AGP), A variant and a mixture of F1S variants. The unbound concentrations of a model basic drug, disopyramide (DP), in A variant solutions and in F1S variant solutions were measured by HPFA-CE to evaluate binding constants at pH 4.0, 5.0, 6.0 and 7.4. The binding between DP and A variant was gradually weakened by acidification of background buffer (from pH 7.4 to 4.0), while the binding between DP and FIS variants decreased at first (from pH 7.4 to 6.0), and then gained (from pH 6.0 to 4.0). Consequently, DP was more strongly bound to A variant than to FIS variants at pH 7.4, while at pH 4.0 DP was more strongly bound to F1S variants. At any pH (S)-DP was bound more strongly than (R)-DP, and the enantioselectivity of A variant was significantly higher than that of F1S variants. Electrophoretic mobilities of the AGP genetic variants decreased along with a decrease in pH. Fluorescent emission of these genetic variants indicated a distinct conformational change between pH 5.0 and 4.0. However, there was no significant difference in the electrophoretic mobility and the fluorescent emission spectrum between these variants at any pH. On the other hand, circular dichroism analyses revealed that beta-sheet content in FIS variants diminished as pH decreased, while that in A variant increased. These results suggest that the conformational change induced by acidification of background buffer differs between these genetic variants, and this causes the difference in DP bindability.

Interindividual variability of the clinical pharmacokinetics of methadone: implications for the treatment of opioid dependence

Methadone is widely used for the treatment of opioid dependence. Although in most countries the drug is administered as a racemic mixture of (R)- and (S)- methadone, (R)-methadone accounts for most, if not all, of the opioid effects. Methadone can be detected in the blood 15-45 minutes after oral administration, with peak plasma concentration at 2.5-4 hours. Methadone has a mean bioavailability of around 75% (range 36-100%). Methadone is highly bound to plasma proteins, in particular to alpha(1)-acid glycoprotein. Its mean free fraction is around 13%, with a 4-fold interindividual variation. Its volume of distribution is about 4 L/kg (range 2-13 L/kg). The elimination of methadone is mediated by biotransformation, followed by renal and faecal excretion. Total body clearance is about 0.095 L/min, with wide interindividual variation (range 0.02-2 L/min). Plasma concentrations of methadone decrease in a biexponential manner, with a mean value of around 22 hours (range 5-130 hours) for elimination half-life. For the active (R)-enantiomer, mean values of around 40 hours have been determined. Cytochrome P450 (CYP) 3A4 and to a lesser extent 2D6 are probably the main isoforms involved in methadone metabolism. Rifampicin (rifampin), phenobarbital, phenytoin, carbamazepine, nevirapine, and efavirenz decrease methadone blood concentrations, probably by induction of CYP3A4 activity, which can result in severe withdrawal symptoms. Inhibitors of CYP3A4, such as fluconazole, and of CYP2D6, such as paroxetine, increase methadone blood concentrations. There is an up to 17-fold interindividual variation of methadone blood concentration for a given dosage, and interindividual variability of CYP enzymes accounts for a large part of this variation. Since methadone probably also displays large interindividual variability in its pharmacodynamics, methadone treatment must be individually adapted to each patient. Because of the high morbidity and mortality associated with opioid dependence, it is of major importance that methadone is used at an effective dosage in maintenance treatment: at least 60 mg/day, but typically 80-100 mg/day. Recent studies also show that a subset of patients might benefit from methadone dosages larger than 100 mg/day, many of them because of high clearance. In clinical management, medical evaluation of objective signs and subjective symptoms is sufficient for dosage titration in most patients. However, therapeutic drug monitoring can be useful in particular situations. In the case of non-response trough plasma concentrations of 400 microg/L for (R,S)-methadone or 250 microg/L for (R)-methadone might be used as target values.

Development of a novel probe for measuring drug binding to the F1*S variant of human alpha 1-acid glycoprotein

A novel probe was developed to measure drug association with the F1*S variant of the human serum protein alpha 1-acid glycoprotein (AGP). The molecule 2-hydroxy-3,5-diiodo-N-[2(diethylamino)ethyl]benzamide (DEDIC) binds to AGP, quenching its native fluorescence. This quenching was fitted to a two-site model giving apparent dissociation constants of 0.049 +/- 0.005 and 12 +/- 2 microM (mean +/- SEM). Quenching of each of the separate variants of AGP by DEDIC was itself described by a two-site model, giving for the F1*S variant K(D)(1)((F1*S)) = 0.041 +/- 0.010 microM and K(D)(2)((F1*S)) = 29 +/- 7 microM; and for the A variant K(D)(1)((A)) = 0.31 +/- 0.18 microM and K(D)(2)((A)) = 8.8 +/- 0.7 microM. The utility of DEDIC in probing drug interactions with isolated variants was demonstrated in competition experiments with the model drugs amitriptyline and bupivacaine. In addition, the selectivity of DEDIC for variant F1*S rendered it capable of probing the binding of drugs (including the variant A-selective drug amitriptyline) to F1*S in a mixture of variants, such as occurs naturally in whole AGP. DEDIC is unique as an F1*S variant-selective probe of drug binding to whole AGP that is also sufficiently soluble to serve as a probe of drug binding to the lower affinity sites on isolated A and F1*S variants.

Role of biantennary glycans and genetic variants of human alpha1-acid glycoprotein in enantioselective binding of basic drugs as studied by high performance frontal analysis/capillary electrophoresis

PURPOSE

To establish a clear understanding of the role of biantennary branching glycans and genetic variants of alpha1-acid glycoprotein (AGP) in enantioselective bindings of basic drug.

METHODS

Human native AGP was separated using concanavalin A affinity chromatography into two subfractions, the unretained fraction (UR-AGP, defect of biantennary glycan) and the retained fraction (R-AGP, possessing biantennary glycan(s)). Imminodiacetate-copper (II) affinity chromatography was used to separate human native AGP into A variant and a mixture of F1 and S variants (F1*S variants). The mixed solutions of the (R)- or (S)-isomer of the model drugs (15 microM disopyramide (DP) or 30 microM verapamil (VER)) and 40 microM of respective AGP species were subjected to high-performance frontal analysis/capillary electrophoresis (HPFA/CE) to determine the unbound drug concentrations.

RESULTS

The unbound concentrations (Cu) of DP in UR-AGP solutions were lower than those in R-AGP solutions, whereas there was no significant difference in the enantiomeric ratios (Cu(R)/Cu(S)) of DP between UR- and R-AGP solutions. In case of genetic variant, the Cu(R)/Cu(S) values of DP in F1*S and A solutions were 1.07 and 2.37, respectively. On the other hand, the enantiomeric ratio of VER in F1*S and A variant solutions were 0.900 and 0.871, respectively.

CONCLUSIONS

The biantennary glycan structures are related to binding affinity of DP to AGP, but not responsible for the enantioselectivity. Genetic variants give significant effect on the enantioselectivity in DP binding, but not in VER binding.

Expression of the genetic variants of human alpha-1-acid glycoprotein in cancer

OBJECTIVES

We have investigated the AAG and its genetic variants concentrations in plasma samples of 61 patients suffering from different types of cancers.

DESIGN AND METHODS

The patients were shared out in three groups, breast, lung, and ovary cancers groups. AAG concentration was measured by an immunonephelometric method and the phenotype was determined, after desialylation of plasma by analytical isoelectric focusing. Detection of AAG variants was made by immunoblotting and their proportions were determined by laser densitometry analysis. A population of 74 healthy individuals served as controls.

RESULTS

The plasma concentrations of AAG in the breast and lung cancer groups were 2.5 times increased, while in the ovary cancer group, the concentrations were 1.6 times increased. AAG concentrations in the cancer population ranged between 0.45 and 2.85 g/L (mean value 1.12 +/- 0.51 g/L). The proportions of the ORM1 and ORM2 variants were similar to those in the healthy population. In breast and lung cancer groups, the relative concentrations of genetic variants were increased more than 2.5 fold, whereas a 1. 6-fold increase was observed in the ovary cancer group.

CONCLUSIONS

These results show that AAG plasma concentrations are increased in these types of cancers and that changes in the expression of the genetic variants of AAG could also occur according to the type of cancer.

Study of the expression of the genetic variants of human alpha1-acid glycoprotein in healthy subjects using isoelectric focusing and immunoblotting

Human alpha1-acid glycoprotein (AAG) exists as an heterogeneous population of two or three genetic variants (ORM1 F1 and/or S and ORM2 A) in the plasma of most individuals. The ORM1 and ORM2 variants have a separate genetic origin. AAG belongs to the acute-phase proteins, which, under conditions of inflammation, increase several-fold in concentration. Additionally, there is evidence to suggest that it is not only the concentration but also the distribution of the two gene products of AAG (ORM1 and ORM2) that alter in such conditions. Variations of the relative concentrations of the AAG variants in certain diseases, such as cancer, can only be shown by reference to data collected in healthy people. In this study, we have investigated a group of 74 healthy subjects (42 men and 32 women) for AAG concentrations, AAG phenotypes and relative proportions of genetic variants in plasma. The specific assay of AAG was carried out by an immunonephelometric method and the phenotyping was performed, after desialylation of AAG, by analytical isoelectric focusing. Detection of the AAG variants was made by immunoblotting and their relative proportions were determined by laser densitometry analysis. The AAG plasma concentrations in the healthy group ranged between 0.28 and 0.92 g/l (mean value 0.50+/-0.14 g/l). The relative proportions of the variants derived from the two genes of AAG were variable, depending on the individual, but the amount of ORM1 variants almost always exceeded that of the ORM2 variant. No sex-related differences were observed in respect either in the total AAG level nor the relative proportions of the ORM1 and ORM2 variants. The data collected in this study may serve as a reference towards the investigation of possible changes in the expression of the genetic variants of AAG in chronic inflammatory diseases.

Changes in expression and microheterogeneity of the genetic variants of human alpha1-acid glycoprotein in malignant mesothelioma

Human alpha1-acid glycoprotein (AAG), an acute-phase plasma protein, is heterogeneous in the native state and polymorphic in the desialylated state. The AAG heterogeneity is mainly explained by a variable glycan chain composition in its five glycosylation sites. The AAG polymorphism is due to the presence of genetic variants. Three main variants are observed for AAG, ORM1 F1, ORM1 S and ORM2 A, which have a separate genetic origin. In this paper, we have used different isoelectric focusing (IEF) methods and chromatography on immobilized metal affinity adsorbent to study the relative occurrence of the genetic variants of AAG in relation to changes in microheterogeneity, in plasma and pleural effusions of patients with malignant mesothelioma (MM). The results were compared to those obtained with the variants in plasma of healthy individuals. Significant changes in variant distribution were observed in the MM samples, that corresponded to a rise in the proportion of the ORM1 variants and a fall in that of the ORM2 variant. However, the concentration in MM plasma increased for both variants. The AAG in MM plasma and effusion fluids was found to be more heterogeneous on IEF than AAG of healthy plasma. The evidence of stronger concentrations of both the high and low pI forms of AAG in the MM samples suggested two kinds of changes in charge heterogeneity. These two changes were shown to be attributed to different variants--i.e. the high pI forms to ORM1 F1 and S and the low pI forms to ORM2 A, after fractionation of AAG by chromatography on immobilized copper(II) ions. These results indicate specific changes in both the expression and glycosylation for each AAG variant, according to its separate genetic origin, in MM.

Ligand specificity of the genetic variants of human alpha1-acid glycoprotein: generation of a three-dimensional quantitative structure-activity relationship model for drug binding to the A variant

Human alpha1-acid glycoprotein (AAG) is a mixture of at least two genetic variants: the A variant and the F1 and/or S variant or variants, which are encoded by two different genes. In a continuation of previous studies indicating specific drug transport roles for each AAG variant according to its separate genetic origin, this work was designed to (1) determine the affinities of the two main gene products of AAG (i.e., the A variant and a mixture of the F1 and S variants) for 35 chemically diverse drugs and (2) to obtain meaningful 3D-QSARs for each binding site. Affinities were obtained by displacement experiments, leading to qualitative indications about binding site characteristics. In particular, drugs binding selectively to the A variant displayed some common structural features, but this was not seen for the F1*S variants. Three-dimensional QSAR analyses using the CoMFA method yielded a steric model for binding to the A variant, from which a simplified haptophoric model was derived. In contrast, no statistically sound model was found for the F1*S variants, possibly due (among other reasons) to an insufficient number of high affinity ligands in the set.

Abnormal microheterogeneity detected in one commercial alpha 1-acid glycoprotein preparation using chromatography on immobilized metal affinity adsorbent and on hydroxyapatite

The study of one commercial preparation of human alpha 1-acid glycoprotein (AAG) by isoelectric focusing and by different chromatographic methods, previously developed to purify and fractionate the genetic variants of AAG, revealed an abnormal heterogeneity for this preparation. In addition to the three main variants (F1, S and A) of AAG normally present, this preparation contained five other AAG variants (called here sigma, alpha, beta, delta and gamma), accounting for ca. 40% of the total. As it is very unlikely that the latter variants are rare AAG variants, the abnormal heterogeneity of this AAG preparation is most probably due to structural alterations occurring during the large scale isolation. The alpha and the sigma, beta, delta and gamma variants could correspond to altered forms of the A and the F1 and S variants, respectively, because of their similar retention behaviour on immobilized copper(II) ions and their similar drug binding properties. However, the elution of the variants from the immobilized metal affinity column suggested that sigma, alpha, beta, delta and gamma were desialylated. Chromatography on hydroxyapatite enabled the separation of the F1, S and A variants from the sigma, alpha, beta, delta and gamma variants. The inability of the latter variants to bind to hydroxyapatite suggests that the structural alterations might involve acidic amino acid residues. This proposal agreed with the isoelectric focusing study of variants sigma, alpha, beta, delta and gamma. Since the different separation methods used were able to resolve the variants of this AAG, this protocol could be used for characterization of commercial AAG proteins.

Two-step chromatographic purification of human plasma alpha(1)-acid glycoprotein: its application to the purification of rare phenotype samples of the protein and their study by chromatography on immobilized metal chelate affinity adsorbent

Alpha1-Acid glycoprotein (AAG) or orosomucoid was purified to homogeneity from human plasma by a separate two-step method using chromatography on immobilized Cibacron Blue F3G-A to cross-linked agarose and chromatography on hydroxyapatite. The conditions for the pre-purification of AAG by chromatography on immobilized Cibacron Blue F3G-A were first optimized using different buffer systems with different pH values. The overall yield of the combined techniques was 80% and ca. 12 mg of AAG were purified from an initial total amount of ca. 15 mg in a ca. 40 ml sample of human plasma. This method was applied to the purification of AAG samples corresponding to the three main phenotypes of the protein (FI*S/A, F1/A and S/A), from individual human plasma previously phenotyped for AAG. A study by isoelectric focusing with carrier ampholytes showed that the microheterogeneity of the purified F1*S/A, F1/A and S/A AAG samples was similar to that of AAG in the corresponding plasma, thus suggesting that no apparent desialylation of the glycoprotein occurred during the purification steps. This method was also applied to the purification of AAG samples corresponding to rare phenotypes of the protein (F1/A*AD, S/A*X0 and F1/A*C1) and the interactions of these variants with immobilized copper(II) ions were then studied at pH 7, by chromatography on an iminodiacetate Sepharose-Cu(II) gel. It was found that the different variants encoded by the first of the two genes coding for AAG in humans (i.e. the F1 and S variants) interacted non-specifically with the immobilized ligand, whereas those encoded by the second gene of AAG (i.e. the A, AD, X0 and C1 variants) strongly bound to immobilized Cu(II) ions. These results suggested that chromatography on an immobilized affinity Cu(II) adsorbent could be helpful to distinguish between the respective products of the two highly polymorphic genes which code for human AAG.

Evidence for differences in the binding of drugs to the two main genetic variants of human alpha 1-acid glycoprotein

1. Human alpha 1-acid glycoprotein (AAG), a plasma transport protein, has three main genetic variants. F1. S and A. Native commercial AAG (a mixture of almost equal proportions of these three variants) has been separated by chromatography into variants which correspond to the proteins of the two genes which code for AAG in humans: the A variant and a mixture of the F1 and S variants (60% F1 and 40% S). Their binding properties towards imipramine, warfarin and mifepristone were studied by equilibrium dialysis. 2. The F1S variant mixture strongly bound warfarin and mifepristone with an affinity of 1.89 and 2.06 x 10(6) l mol-1, respectively, but had a low affinity for imipramine. Conversely, the A variant strongly bound imipramine with an affinity of 0.98 x 10(6) l mol-1. The low degree of binding of warfarin and mifepristone to the A variant sample was explained by the presence of protein contaminants in this sample. These results indicate specific drug transport roles for each variant, with respect to its separate genetic origin. 3. Control binding experiments performed with (unfractionated) commercial AAG and with AAG isolated from individuals with either the F1/A or S/A phenotypes, agreed with these findings. The results for the binding of warfarin and mifepristone by the AAG samples were similar to those obtained with the F1S mixture: the mean high-affinity association constant of the AAG samples for each drug was of the same order as that of the F1S mixture: the decrease in the number of binding sites of the AAG samples, as compared with the F1S mixture, was explained by the smaller proportion of variants F1 and/or S in these samples. Conversely, results of the imipramine binding study with the AAG samples concurred with those for the binding of this basic drug by the A variant, with respect to the proportion of the A variant in these samples.

Subtyping of alkylated human orosomucoid: evidence for a duplicated gene, ORM1*F2S

Isoelectric focusing of human orosomucoid (ORM) was studied following different sample treatment. It is shown that: (i) alkylation with iodoacetamide leads to a drastic change in the isoelectric point (pI) of both ORM1 F2 and ORM2 A gene products and greatly improves the discrimination between ORM1 F1 and ORM1 F2; (ii) previous reduction of the molecule with dithiothreitol partially inhibits the pI transitions with resultant artifactual ORM1 F1F2S patterns that correspond in most cases to F2S phenotypes. With the technique now described, the persistence of three ORM1 gene products was found in only one individual and the segregation analysis is consistent with the existence of a rare ORM1*F2S haplotype.

Orosomucoid system: 17 additional orosomucoid variants and proposal for a new nomenclature

There are two forms of orosomucoid (ORM) in the sera of most individuals. They are encoded by two separate but closely linked loci, ORM1 and ORM2. A number of variants have been identified in various populations. Duplication and nonexpression are also observed in some populations. Thus, the ORM system is very complicated and its nomenclature is very confusing. In order to propose a new nomenclature, ORM variants detected by several laboratories have been compared and characterized by isoelectric focusing (IEF) followed by immunoprinting. A total of 57 different alleles including 17 new ones were identified. The 27 alleles were assigned to the ORM1 locus, and the others to the ORM2 locus. The designations ORM*F1, ORM1*F2, ORM1*S and ORM2*M were adopted for the four common alleles instead of ORM1*1, ORM1*3, ORM1*2 and ORM2*1 (ORM2*A), respectively. The variants were designated alpha numerically according to their relative mobilities after IEF in a pH gradient of 4.5-5.4 with Triton X-100 and glycerol. For the duplicated genes a prefix is added to a combined name of two alleles, e.g. ORM1*dB9S. Silent alleles were named ORM1*Q0 and ORM2*Q0 conventionally. In addition, the effects of diseases to ORM band patterns after IEF are also discussed.

Inflammation-induced changes in expression and glycosylation of genetic variants of alpha 1-acid glycoprotein. Studies with human sera, primary cultures of human hepatocytes and transgenic mice

The relative occurrence of genetic variants of human alpha 1-acid glycoprotein (AGP) in relation to changes in glycosylation was studied in sera of patients with burn injury, media of cytokine-treated primary cultures of human hepatocytes and Hep 3B cells, and sera of transgenic mice expressing the human AGP-A gene. It is concluded (i) that the glycosylation of AGP was not dependent on its genetic expression and (ii) that both the variants determined by the AGP-A gene as well as by the AGP-B/B' genes are increased after inflammation or treatment with interleukins 1 and 6.

Orosomucoid typing by isoelectric focusing: genetic variation of orosomucoid in Asian macaques (genus Macaca)

Genetic variation of orosomucoid (ORM) in the genus Macaca was investigated. Plasma samples were subjected to isoelectric focusing in a pH range of 4-6.5, followed by immunoprinting with anti-human ORM antibodies. A total of 25 alleles were identified in 231 Asian macaques belonging to 13 species from 23 populations and 22 members belonging to a family of M. fascicularis. Family data presented evidence for a codominant mode of inheritance with multi-alleles at a single autosomal locus. A population study revealed enormous intra- and interspecies variations. The heterozygosity values varied from 0.855 in M. fascicularis (Malaysia) to 0.000 in M. radiata (India), M. silenus (India) and M. arctoides (Malaysia).