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Biomedical subjects

R Brodersen

Publications and source records attributed to R Brodersen.

At least 55 records · Page 3Linked to original sources
PubMed1986

A two-constant equation for multiple albumin-binding isotherms.

It has been found that binding of low molecular weight ligands to human serum albumin is generally nonsaturating. Equations commonly used for describing the binding equilibria, i.e., the Scatchard and Klotz (Adair) equations, are saturation functions. We have accordingly tried to establish an equation which would fit the observed data, i.e., not reach a saturation plateau. An empirical equation, in which the bound ligand is expressed as a function of the free ligand [R(C) = b1 in (b2C + 1)], is shown to give reasonably good fits to observed binding equilibrium data for the binding of several organic ligands to human serum albumin, when the two parameters, b1 and b2, are given suitable values. The curve of bound versus free ligand, as plotted from this equation, has the same slope and curvature as that obtained from the Klotz stepwise binding equation at C = 0, if b1 = K1/[2(K1 - 2K2)] and b2 = 2(K1 - 2K2), where K1 and K2 are the first and second stoichiometric binding constants.

Albumins↗
PubMed1986

Spectroscopic properties of bilirubin-human serum albumin complexes: a stoichiometric analysis.

Light absorption spectra, fluorescence of bound bilirubin, fluorescence of albumin as quenched by bilirubin, and circular dichroism spectra have been studied in mixtures of bilirubin and defatted human serum albumin in variable proportions at 25 degrees C and at pH 7.4, 8.2, and 9.0. Corresponding spectral data have been calculated for the stoichiometric bilirubin-albumin complexes, 1:1, 2:1, and 3:1. Light absorption spectra as well as the bound bilirubin fluorescence indicate that all three bound bilirubin dianions are internalized. These data were obtained by curve fitting to least sum of squared deviations. In addition to the best fit we obtained 30 acceptable curves, located within an F contour, thus producing a rough estimate of the variation of the resulting spectral data.

Bilirubin↗
PubMed1986

Warfarin binding to plasma albumin, measured in patients and related to fatty acid concentrations.

A method for determination of reserve albumin equivalent for binding of warfarin as previously described [1] has been used for assessing the influence of non-esterified fatty acid concentration (NEFA) on binding of warfarin to human serum albumin (HSA). Reserve albumin concentration can be used for calculation of the expected fraction of bound warfarin in serum. It is shown in vitro that binding of warfarin increases with added oleate up to 4 mol of oleate per mol of albumin and then decreases. Twenty-four patients on permanent warfarin treatment showed no correlation of serum albumin and reserve albumin concentrations (r = 0.10, P greater than 0.50) indicating that warfarin binding is governed by other factors. However, in the same patients there was a significant correlation between reserve albumin concentration and NEFA/HSA (r = 0.54, P less than 0.01). In one human volunteer changes of NEFA were provoked by strenuous work and it was found that reserve albumin concentration increased with NEFA concentration as expected from the in vitro findings (r = 0.90, P less than 0.001). Five uraemic patients on permanent warfarin treatment showed increasing reserve albumin concentration with increasing NEFA concentration induced by heparin. These findings indicate that, both in vitro and in vivo, the reserve albumin concentration for binding of warfarin and hence the free warfarin concentration is markedly influenced by NEFA concentration. This may add to the understanding of warfarin dose requirement during anticoagulant therapy.

Adult↗
PubMed1986

Reduced albumin binding of MADDS--a measure for bilirubin binding--in sick children.

The reserve albumin concentration for binding of MADDS (monoacetyldiaminodiphenyl sulphone) in plasma is used as a measure of the reserve albumin concentration for binding of unconjugated bilirubin. The aim of the present study was to investigate whether a reduction in the reserve albumin concentration for binding of MADDS could exist in sick children after 5 months of age, where the bilirubin binding properties of the albumin has reached the adult level. The material included 75 children, 1-15 years of age with mild infections, severe bacterial infections, acute viral hepatitis, chronic hepatic diseases or uraemia, and a control group of 22 healthy children. The reserve albumin concentration was significantly lower in children with severe bacterial infections, acute viral hepatitis, and uraemia, than in healthy children (p less than 0.01), while the reserve albumin concentration in children with mild infections and chronic hepatic diseases did not differ significantly from that of the control group (p greater than 0.05). The total albumin concentration in plasma in either of the groups of sick children did not differ significantly from that of the healthy children. The plasma concentration of unconjugated bilirubin was elevated in the group of children with acute viral hepatitis, but not enough to influence the concentration of reserve albumin for binding of MADDS to a significant degree. The reserve albumin concentration was significantly lower in children with acute viral hepatitis than in children with severe bacterial infections (p less than 0.05).

Adolescent↗
PubMed1986

Bilirubin/rat serum albumin interaction.

Essential differences are demonstrated between bilirubin binding to rat serum proteins and to albumin in human serum. Acidimetric titration of rat serum with and without added bilirubin shows that binding of bilirubin acid in the range of pH from 6.8 to 8.8 takes place with release of less than one hydrogen ion per molecule of bound bilirubin. With human serum, two hydrogen ions are released, indicating binding of bilirubin dianion. The binding equilibrium of N-[4-[(4-aminophenyl)-sulfonyl]phenyl]-acetamide (MADDS) to rat serum albumin is influenced slightly by cobinding of bilirubin whereas MADDS and bilirubin bind competitively to human serum albumin. Finally, the rate of oxidation of bilirubin with hydrogen peroxide and peroxidase is decreased moderately by addition of rat serum albumin and strongly by the human protein, indicating that biliribin in its complex with rat serum albumin is subject to oxidation while the complex with human serum albumin is protected. These differences should be considered when rats are used as a model in experimental studies aiming at prevention of bilirubin encephalopathy in human neonates.

Animals↗
PubMed1985

Multiple cobinding of two ligands to serum albumin: a stoichiometric description of binding equilibria.

Binding equilibria for simultaneous binding of several molecules of two anionic ligands, sulfamethizole/warfarin in one series and sulfamethizole/diflunisal in another, to human serum albumin were studied by equilibrium dialysis. It was found that Klotz's stepwise binding equilibrium concept, extended to cover interaction of two ligands with one carrier, could be used for a quantitative description of binding equilibria. Reciprocity of ligand effects was established at all levels. Heterotropic anticooperativity was present among these pairs of ligands. The experiments were supplemented with observations of albumin binding equilibria for traces of warfarin in the presence of varying amount of oleate, up to 6 mol/mol albumin, by measuring dialysis rates for unbound warfarin. Binding of warfarin to albumin is enhanced upon binding of oleate up to 4 mol/mol albumin, and decreases at higher oleate concentrations. Using stoichiometric (stepwise) binding constants for oleate previously published by Ashbrook et al. [(1975) J. Biol. Chem. 250, 2333-2338], the reverse effect, of warfarin on binding of oleate, was calculated. Simultaneous binding of these ligands to albumin could be described according to the stoichiometric principles as used above for sulfamethizole/warfarin and sulfamethizole/diflunisal.

Binding, Competitive↗
PubMed1985

Fusidic acid binding to serum albumin and interaction with binding of bilirubin.

Sodium fusidate, an antibiotic used in staphylococcal infections, is strongly bound to human serum albumin, competitively with bilirubin. It is given in molar amounts sufficient to occupy a considerable fraction of circulating albumin. In order to avoid a risk of bilirubin encephalopathy, induced by displacement of bilirubin, fusidate should be given with caution to newborn infants, particularly if patients are prematurely born, icteric or acidotic. Fusidate does not interfere with albumin binding of warfarin or diazepam.

Adult↗
PubMed1985

Interaction of warfarin with human serum albumin. A stoichiometric description.

Reversible binding of warfarin to defatted serum albumin was studied by equilibrium dialysis at pH 7.4, in a 66 mM sodium phosphate buffer at 37 degrees. The binding isotherm could be described by two stoichiometric binding constants, K1 in the range 141,000 to 192,000 M-1 and K2 at 39,000 to 57,000 M-1. At least two additional molecules could be bound but gave indeterminate binding constants. The product K3 X K4 was about 4.7 X 10(7) M-2. Different site models were possible, either one high affinity and several low affinity sites, or two high affinity sites, cooperative, independent, or anticooperative, together with two low affinity sites. Binding affinity for the first warfarin molecule did not vary with pH in the interval from 6 to 9. The affinity decreased with increasing concentrations of sodium sulfate, sodium chloride, and calcium chloride, depending upon ionic strength. Specific effects of chloride and calcium ions were not observed. Light absorption spectra indicated that the warfarin anion was bound to albumin. All observations were consistent with a binding process involving albumin and the warfarin anion, without participation of hydrogen ions and not influenced by the N-B conformational transition of albumin.

Electrolytes↗
PubMed1984

Serum albumin--a non-saturable carrier.

The shape of binding isotherms for sixteen ligands to human serum albumin showed no signs of approaching saturation at high ligand concentrations. It is suggested that ligand binding to serum albumin is essentially different from saturable binding of substrates to enzymes, of oxygen to haemoglobin, etc. Binding to serum albumin appears to be non-saturable.

Bilirubin↗
PubMed1984

Warfarin-sulfinpyrazone interaction on binding to human serum albumin.

Sulfinpyrazone displacement of warfarin from human serum albumin was studied in-vitro. At low sulfinpyrazone concentrations one molecule of warfarin is displaced on binding by one molecule of sulfinpyrazone. Clinical plasma concentrations of sulfinpyrazone are, however, too low to cause significant displacement.

Binding, Competitive↗
PubMed1984

Albumin binding of anti-inflammatory drugs. Utility of a site-oriented versus a stoichiometric analysis.

Binding equilibria of 12 nonsteroidal, anti-inflammatory substances, salicylic acid, diflunisal, phenylbutazone, azapropazone, fenbufen, biphenylacetic acid, naproxen, flurbiprofen, ibuprofin, diclofenac, indomethacin, and benoxaprofen, to defatted human serum albumin has been investigated at 37 degrees, pH 7.4, in a sodium phosphate buffer, 66 mM, by means of equilibrium dialysis and, in case of salicylic acid, by dialysis rate determinations. Cobinding of each of these drugs with monoacetyl-4,4'-diaminodiphenyl sulfone, warfarin, and diazepam has been studied by measuring dialysis rates of the last-mentioned ligands. Cobinding of each drug with bilirubin was investigated by two techniques, equilibrium dialysis against albumin with and without bilirubin, and by measuring rates of oxidation of free bilirubin with hydrogen peroxide and peroxidase. Results were analyzed in quantitative terms. The use of a site-oriented description versus a stoichiometric analysis is discussed. The stoichiometric description is preferred for the following reasons: (a) Simple relations exist between the percentage of bound drug at low drug concentrations and the first stoichiometric binding constant. (b) The stoichiometric description does not imply that preformed binding sites are present in the albumin molecule. (c) A quantitative, stoichiometric analysis of multiple cobinding of two ligands is possible.

Anti-Inflammatory Agents↗
PubMed1983

Albumin-bilirubin binding mechanism.

After binding of bilirubin to human serum albumin (1:1), a train of relaxational changes of conformation takes place. The late part of these processes, occurring in the time interval 1-500 s, has been studied by recording the changes of light absorption. Similar processes have been demonstrated after binding of fatty acid anion to the bilirubin-albumin complex as well as after a pH-jump from 6 to 9. Solvent perturbation spectra obtained on the addition of 20% sucrose have failed to demonstrate exposure of the bilirubin chromophores in the complex to the surrounding medium. Xanthobilirubinate which has a single dipyrrolic chromophore compared to the two of bilirubin is bound to albumin in competition with bilirubin, as concluded from co-binding studies with monoacetyldiaminodiphenylsulfone and diazepam, probing two different binding functions of the albumin molecule. Late conformational changes were absent after binding of xanthobilirubinate. Binding of fatty acid to the complex and a pH-jump did not affect the spectrum of xanthobilirubinate-human serum albumin. The findings can be explained by a model, previously proposed, in which the late spectral changes are affected by rotation of one half-domain of albumin, binding one bilirubin chromophore, relative to another half-domain to which the second bilirubin chromophore is bound, whereby a change of exiton splitting occurs. Such changes are not seen with the complex of xanthobilirubinate and albumin, since only a single chromophore is present.

Bilirubin↗
PubMed1983

Bilirubin-displacing effect of ampicillin, indomethacin, chlorpromazine, gentamicin, and parabens in vitro and in newborn infants.

Displacement of bilirubin bound to human serum albumin by ampicillin, indomethacin, chlorpromazine, gentamicin, methylparaben, and propylparaben was investigated quantitatively. Two methods were used in vitro: measurement of bilirubin displacement by studying the rate of bilirubin oxidation with hydrogen peroxide and peroxidase and determination of the albumin reserve for binding of bilirubin by observation of the dialysis rate of an added trace amount of a deputy ligand monoacetyldapsone (p-acetamido-p'-aminodiphenyl sulfone). The latter method was also used for the determination of the albumin reserve in sera from treated newborn infants. The following doses were given: ampicillin, 100 mg/kg iv; indomethacin, 0.2 mg/kg iv; chlorpromazine hydrochloride, 0.7 mg/kg im; gentamicin sulfate, 2.5 mg/kg im. The parabens were present in injectable preparations of chlorpromazine and gentamicin and were therefore given in the following doses: methylparaben, 0.35 mg/kg, and propylparaben, 0.05 mg/kg. All drugs were given in a single dose. A few additional additives and metabolites were studied in vitro. Ampicillin, given to 19 infants, produced a small, significant decrease in plasma albumin reserve, to 82% of the pretreatment level and, thus, had a slight bilirubin-displacing effect, quantitatively consistent with a weak displacing effect measured in vitro. None of the other substances showed any measurable displacement in vivo, likewise in agreement with the results from in vitro studies.

Ampicillin↗
PubMed1983

Effect of lactate, pyruvate, acetone, acetoacetate, and beta-hydroxybutyrate on albumin binding of bilirubin.

Lactate, pyruvate, acetone, acetoacetate, and beta-hydroxybutyrate were tested for their bilirubin-displacing effect on human serum albumin. Only lactate had a significant effect at levels found in asphyxiated infants (up to 20 mM). The reserve albumin equivalent for binding bilirubin was determined, using the deputy ligand monoacetyldiaminodiphenyl sulfone (MADDS), in adult human serum albumin solution, neonatal serum, and neonatal albumin solution. Twenty mM lactate caused a 23% decrease of reserve albumin when adult albumin was used, but did not cause any change of binding when neonatal serum or neonatal albumin solution was used. It is unlikely that endogenous substances, acting as competitive ligands, cause the low binding affinity of albumin for bilirubin in sick, premature infants.

3-Hydroxybutyric Acid↗
PubMed1983

Reserve albumin and bilirubin toxicity index in infant serum.

Reserve albumin concentration (the concentration of albumin available for binding of unconjugated bilirubin) was determined in 95 sera from 76 subjects by dialysis with 14C-monoacetyl diamino diphenyl sulfone (MADDS). An index, I of bilirubin toxicity in the plasma was calculated for each subject, based on the bilirubin and reserve albumin concentrations, the affinity of bilirubin for serum albumin, and the pH-dependent solubility of bilirubin in the plasma. The values of reserve albumin and of I varied significantly with gestational age, clinical condition (whether sick or well), and serum bilirubin level. The value of reserve albumin was decreased and I was increased in association with clinical factors (e.g., hyperbilirubinemia, hypoxia, acidosis, or sepsis) recognized as increasing the risk for bilirubin encephalopathy. The lowest values of reserve albumin and the highest values of I were found in the least mature and sickest infants.

Adult↗
PubMed1983

Drug-induced displacement of bilirubin from albumin in the newborn.

Kernicterus is probably caused by precipitation of insoluble bilirubin acid in brain cells. The pigment is transferred from blood plasma to cells. The tendency for precipitation depends upon the ratio of unconjugated plasma bilirubin concentration to the concentration of reserve albumin for binding of bilirubin and is increased when part of the albumin is occupied by competitive binding of a drug. Laboratory methods are available whereby it is possible, on certain well-defined presumptions, to measure this drug effect in quantitative terms. Measurements can be made in systems with pure albumin as well as in plasma samples from treated patients. It would thus appear feasible at the present stage to establish a basis for official testing of the bilirubin-displacing effects of drugs.

Bilirubin↗
PubMed1983

Bilirubin-displacing effect of furosemide and sulfisoxazole. An in vitro and in vivo study in neonatal serum.

Sulfisoxazole and furosemide, 0.1-1.0 mM, both decreased reserve albumin concentration for bilirubin binding in pooled cord serum as estimated by rate of dialysis of 14C-monoacetyl-diamino-diphenylsulfone (MADDS) in undiluted serum at 37 degrees C. Peroxidase oxidation at a bilirubin:albumin ratio of 0.5 also showed that both drugs were capable of displacing bilirubin in vitro when added in molar excess of the albumin present. However, when aliquots of the same treated sera which had been used undiluted in the MADDS assay were diluted 40-fold and titrated with bilirubin and peroxidase, no drug-related increase in free bilirubin or decrease in reserve albumin could be shown. In vivo administration of 1 mg/kg furosemide showed no change in total bilirubin or reserve albumin by the MADDS technique in 8 infants. Estimation of the peak plasma level theoretically achievable with 1 mg/kg of furosemide suggests that peak plasma levels achieved with that dose are probably not high enough to produce significant reduction of reserve albumin, in agreement with the in vivo findings. In testing neonatal serum for bilirubin displacement by drugs, the choice of method, drug concentration, and dilution of the sample may influence the interpretation of results.

Bilirubin↗