Biomedical subjects
Publications and source records attributed to S Urien.
Kinetics of trans- and cis-resveratrol (3,4',5-trihydroxystilbene), a natural compound from grape products, have been evaluated in rats after oral administration of red wine. Resveratrol concentrations were measured in plasma, heart, liver and kidneys. Tissue concentrations showed a significant cardiac bioavailability and strong affinity for liver and kidneys.
Eight ligands were used in this study, four basic, three neutral and one acidic. Their binding to serum alpha 1-acid glycoprotein (orosomucoid) was measured at several temperatures, and the data were analysed together by a general model with three unknowns, number of binding sites, delta H0 and delta S0. The partition coefficients of the ligands were measured in octanol/water and heptane/water systems (log Poct. and log Phep.), and their molecular volumes were calculated by molecular modelling techniques. These structural properties allow determination of polarity parameters (delta log Poct.-hep., lambda oct. and lambda hep.) which encode in different proportions the various polar interactions between the solute and the aqueous and organic phases, i.e. hydrogen-bonding capacity and dipolarity/polarizability. This study shows that good correlations exist between delta H0 or delta S0 and polarity parameters, such that the enthalpic contribution to binding increases with increasing polarity of the ligands, mainly hydrogen-bond-donor acidity, whereas their entropic contribution to binding decreases.
The interactions of S9788 with human plasma proteins have been investigated in vitro by an erythrocyte partitioning technique that allows an estimation of the plasma proteins and erythrocytes binding parameters. S9788 was 98% bound to plasma and blood. Lipoproteins bound S9788 with high affinities (binding constants of 0.645, 12.8 and 87.0 x 10(6) M-1 for HDL, LDL and VLDL, respectively) and accounted for more than 55% of the total circulating S9788. Albumin and alpha 1-acid glycoprotein also bound S9788 with lower binding constants of 0.022 and 0.245 x 10(6) M-1. S9788 was mainly distributed in the plasma blood compartment (75-80%) with blood-to-plasma concentrations ratio of 0.6 to 0.7. These results indicate that, in vivo, the fraction of blood S9788 available for tissue diffusion, i.e., the free drug fraction in blood, should depend on lipoprotein concentration in plasma.
PURPOSE: The microcomputer program, MicroPharm-K (MP-K) was developed for pharmacokinetic modeling, including analysis of experimental data and estimation of relevant parameters, and simulation. The intention was to provide a user-friendly, interactive, event-driven program for PC computers. METHODS: The data are ascribed to a predefined model from a library including various routes of administration, oral or intra-venous, bolus or infusion, and various compartmental interpretations, 1 to 3. Single and multiple administrations are supported. The program provides initial estimates of the parameters in most cases, and the parameters are then fitted to the model by non linear model fitting using either the Simplex, Evol, Gauss-Newton, Levenberg-Marquardt or Fletcher-Powell algorithms. The non linear model fitting is based on the maximum likelihood method, and the criterion to minimize is either the weighted least squares (Chi 2 criterion) or the extended least squares. Graphical representations of non-fitted or curve-fitted data are immediately available (including log-scale representation), as well as pharmacokinetic typical parameters such as area under the curve, clearance, volumes, time-rate constants, transfer rate constants, etc. RESULTS: Simulated and experimental data were analysed and the results were similar to those obtained by other programs. CONCLUSIONS: This non linear fitting program has been proved in our laboratory to be a very effective package for pharmacokinetic studies, including estimation and simulation. Because it is easy-to-use and runs on basic computers, the program could also be used for educational purposes.
The binding interactions of four ligands differing in acid-base properties with human serum albumin (HSA) were examined as a function of temperature. Binding to HSA decreased with increasing temperature for all four ligands. The bound and free ligand concentrations obtained at different temperatures were satisfactorily fitted to a model that incorporates the effect of temperature as an independent covariable and that directly allows the estimation of the enthalpic and entropic components of the ligand-albumin interaction, along with the precision of this estimation. Using this analysis, the binding of acidic ligands could be resolved into two classes of saturable sites, with the determination of the corresponding number of sites, whereas interpretation of binding data at each isolated temperature allowed only the determination of one saturable plus one non-saturable class of site. The thermodynamic constants indicate that binding of ionizable ligands to HSA involves electrostatic plus hydrophobic interactions, whereas only hydrophobic interactions are involved in binding to a second low-affinity class of site when present. Binding of non-ionizable ligands resembles that of the second class of low-affinity sites of ionizable ligands.
The binding of methotrexate to human serum albumin and the inhibitory effect of serum free fatty acids (FFA) have been studied by equilibrium dialysis with radiolabeled methotrexate. Methotrexate was bound to albumin via a single site (1.03 +/- 0.02) with a low affinity (1350 +/- 60 M-1). The effect of FFA on binding by albumin of methotrexate was analysed according to the classical inhibition models with computation of the free inhibitor concentration and was ascribed to an uncompetitive type of inhibition. These results were in agreement with the observed serum binding of methotrexate (45-50%) and allowed the simulation of the effect of various concentrations of FFA on methotrexate albumin binding in human serum.
The location of labelled probucol in lipoprotein particles was investigated in-vitro. Human serum was incubated for 4 h at 37 degrees C with [14C]probucol to incorporate probucol into lipoproteins. Serum lipoprotein particles were then isolated according to their apolipoprotein markers by sequential immunoaffinity chromatography at 4 degrees C, and probucol concentration was determined in each lipoprotein fraction. Analysis of probucol distribution vs lipoprotein components revealed that probucol in particles strongly correlated with phospholipid concentration. Analysis of probucol distribution vs lipoprotein physical characteristics showed that probucol strongly correlated with the surface area of the monolayer surrounding the lipidic core of particles constituting phospholipids and free cholesterol. These data support the hypothesis that probucol is preferentially located in the phospholipid/free cholesterol monolayer surrounding the lipid core, in the vicinity of cholesteryl ester at the core surface or in the vicinity of hydrophobic areas of apolipoprotein that faces the monolayer.
The ligands are generally bound in plasma to a significant extent by several transport proteins (both high and low affinity), irrespective of their endogenous or exogenous origin. The protein binding of endogenous compounds (such as hormones) exhibits higher affinity and specificity than those of exogenous compounds (such as drugs). For plasma proteins that bind the same ligand(s), structural similarities or a common genetic origin may be found, although this is not a general rule. Alterations in ligand binding may be due to modifications of either the structure or the level of the binding protein. These modifications may result from genetic make up, physiology or pathology. In some situations, plasma binding may impair the distribution of drugs to tissues, with drug distribution then mainly restricted to the distribution compartment of the drug-binding protein. In other instances, the plasma drug-binding is permissive, and does not limit drug distribution to tissues. A given drug-transport protein system may have either a permissive or a restrictive effect on the drug distribution, depending on the tissue. The physiological significance of the high-affinity transport proteins is not completely understood. These proteins may increase the plasma concentration of poorly hydrosoluble ligands, ensure a more uniform tissue distribution and increase the life of the ligands. The life of the protein may also be increased by ligand binding. High-affinity transport proteins are also involved in some specific carrier mediated transfer mechanisms. It is possible to demonstrate structure-binding relationships or binding selectivity for the plasma transport proteins, but these are quite independent of relationships observed at the receptor level.
The interactions of ten retinoid derivatives with human serum albumin (HSA) and lipoproteins have been investigated in vitro by an erythrocyte-partitioning technique that allows a quantitative estimation of the protein and erythrocyte binding. It was found that all these compounds were highly bound to HSA and lipoprotein. The binding to HSA was superior or similar to the binding to lipoprotein in the case of carboxylic acid derivatives. For the neutral derivatives, the binding to lipoproteins was generally higher than the binding to HSA. Retinoid binding to lipoproteins was strongly related to the computed octanol water partition coefficient (CLOGP).
The serum binding of methotrexate was determined by equilibrium dialysis using radiolabelled methotrexate. Methotrexate was only albumin-bound in serum. The binding was 46% in controls versus 42% in rheumatoid arthritis and 44% in cancer. Serum binding was significantly decreased by salicylate and high concentration of naproxen. Hypoalbuminemia and concomitant administration of salicylate or naproxen may influence methotrexate toxicity.
The binding of warfarin to alpha 1-acid glycoprotein (AAG) was found to increase with decreasing pH. The u.v.-visible difference spectra generated upon binding to AAG at pH 5.0 or 7.4 showed warfarin to bind as the anion. Warfarin-binding data were satisfactorily fitted to a model that incorporates the effect of pH and discriminates the association constants of the non-protonated and protonated binding site of the protein. It was shown that AAG-binding site in the protonated form had a markedly higher affinity for warfarin than the non-protonated form, with a pK value of 7.7 +/- 0.1, which is likely to be a histidine residue. Among other possible interactions, it is suggested that ligand binding to AAG involves a reinforced hydrogen bond.
Human serum albumin is known to be the main carrier of 5-methoxypsoralen (5-MOP) in serum. As hypoalbuminaemia may occur in psoriasis with inflammatory syndrome, variability of the free 5-MOP fraction in serum can be expected. The free 5-MOP fraction was determined by equilibrium dialysis in serum samples obtained from 18 psoriatic patients and 18 control subjects. The median free 5-MOP fraction was not significantly different in the psoriatic group (fu = 4.75%) than in the control group (fu = 5%). However, there was a significantly larger variability of the free fraction in the psoriatic group (2.7 to 8.6%) than in the healthy group (3.2 to 6.8%) (p = 0.002). The binding index of 5-MOP (ratio of bound to free concentrations) was correlated with human serum albumin level (r = 0.784). This work confirms that the 5-MOP fraction in human serum is principally serum albumin dependent, as has been described with in vitro models. Free drug monitoring of 5-MOP is discussed.
Using [3H]-vinorelbine, we demonstrated the presence of saturable and time-dependent high-affinity binding sites on human platelets and lymphocytes. The dissociation constant and binding-site values observed were 200 +/- 38 nM, 20.0 +/- 2.2 amol/platelet, and 155 +/- 20 amol/lymphocyte, respectively. Among other blood components, saturable low-affinity binding of vinorelbine to alpha 1-acid glycoprotein, serum albumin, and lipoproteins was observed. The binding to erythocytes was nonsaturable. Given the relative concentrations of these carriers, vinorelbine mainly distributes in the platelet compartment in blood (> 70%), and the amount of free vinorelbine in plasma relative to the total amount in blood is < 2%. It is suggested that because of the preferential retention of vinorelbine by platelets, variations in the platelet count are very likely to produce changes in the free blood fraction of vinorelbine.
Tertatolol, a recently developed beta 1-beta 2-blocker has two advantages: it does not induce withdrawal syndrome after abrupt cessation, and it preserves renal function. It has been suggested that the kinetics of tertatolol in patients with hepatic dysfunction are altered. Therefore, the hemodynamic effects and pharmacokinetics following the acute administration of tertatolol were studied in cirrhotic patients with portal hypertension. Systemic, splanchnic and renal hemodynamics were evaluated before and 30 min after the simultaneous administration of 2.5 mg tertatolol p.o. and 1.25 mg deuterated tertatolol i.v. in 10 cirrhotic patients with esophageal varices. The pharmacokinetics of tertatolol were evaluated over a 4-day period. Tertatolol significantly decreased heart rate (-22 +/- 10%), cardiac output (-26 +/- 8%), and hepatic blood flow (-27 +/- 23%). The hepatic venous pressure gradient decreased from 15.7 +/- 5.0 to 12.9 +/- 4.0 mmHg (-17 +/- 13%, P < 0.01). Three out of 10 patients were non-responders to tertatolol. Renal blood flow (-9 +/- 28%) and intrinsic hepatic clearance of indocyanin green (-9 +/- 25%) were not significantly modified. The duration of effective beta-blockade was far less than 12 h. Tertatolol was rapidly absorbed with a Cmax of 70 +/- 51 micrograms/l at a peak time of 0.75 +/- 0.26 h. In comparison with healthy volunteers referred to in literature sources, plasma clearance was reduced to 49 +/- 28 ml/min, bioavailability was increased to 72 +/- 20%, and the volume of distribution was increased to 50 +/- 34 l, probably due, in part, to a weaker protein binding -85%--effect.(ABSTRACT TRUNCATED AT 250 WORDS)
The binding of tenoxicam to human serum albumin has been shown by affinity chromatography proton titration and equilibrium dialysis to be dependent on the neutral to basic conformational change of the protein. The influence of diazepam on the interaction was also investigated using the same techniques, suggesting that diazepam increases the association of tenoxicam to albumin. Affinity chromatography revealed that the reciprocal effect also occurs. Displacement studies indicated that diazepam causes a significant increase in the affinity of tenoxicam to its main binding site, albumin site I, which is different from the diazepam site (site II). Tenoxicam seemed to cause an allosteric change in the conformation of the protein during its own binding, as did warfarin. The mechanism of this effect was a pH-dependent conformational change of albumin induced by electrostatic forces within the protein. Diazepam induced a distant accommodation of the protein, an effect accompanied by an enhanced inhibition of the release of protons from albumin.
The binding of nimesulide within human serum to isolated proteins and to erythrocytes was studied by equilibrium dialysis. Within the range of therapeutic concentrations, nimesulide was 99% bound to serum involving a nonsaturated process (NKA = 91). This binding was almost identical to binding of nimesulide to serum albumin (NKA = 95). Physiological concentrations of free fatty acids did not affect binding of nimesulide to serum albumin. The retention of nimesulide by erythrocytes suspended in buffer was moderate (67%), although in whole blood no erythrocyte binding was observed because of the greater affinity of this drug for serum. Over the range of therapeutic concentrations (2.5 to 63 mumol/L), the free fraction of nimesulide in serum remains constant. Serum binding was decreased in samples obtained from patients with renal failure or hepatic cirrhosis associated with hypoalbuminaemia and hyperbilirubinaemia, respectively. At therapeutic concentrations, the binding of nimesulide was unaffected by warfarin, cefoperazone, furosemide (frusemide), glibenclamide, tamoxifen or digitoxin. However, valproic acid and fenofibrate (80 mumol/L) may displace nimesulide. 4-Hydroxy-nimesulide, the principal metabolite, significantly increased the free fraction of nimesulide. Although methotrexate had no effect on the free fraction of nimesulide, the free fraction of methotrexate was significantly increased in the presence of nimesulide. The present study also demonstrated 2 distinct nimesulide binding sites (site I and site II) on serum albumin (10 mumol/L) with different affinities: site II KA = 3.57 x 10(5) L/mol and site I KA = 1.24 x 10(5) L/mol. Interaction studies using markers that bind specifically to site I (warfarin and azapropazone) and site II (diazepam and ibuprofen) indicated that nimesulide binds to site II with higher affinity and to a lesser extent to site I.
The binding of 5-methoxypsoralen (5-MOP) to human serum and blood fractions was studied by equilibrium dialysis associated to high-performance liquid chromatography. 5-MOP serum binding was 95% and kept constant in the range of therapeutic concentrations. Albumin was the main binding protein with one class of binding sites (n = 2.05) and with a moderate affinity constant (Ka = 10,270 M-1). Free fatty acids (FFA) enhanced 5-MOP binding to albumin. Binding to other proteins, alpha 1-acid glycoprotein, gamma-globulins and lipoproteins (LDL, HDL, VLDL) also occurred, but was negligible. 5-MOP bound to red blood cells (RBCs) with a binding index (ratio of intra- to extra-globular 5-MOP concentrations) of 3.84 and 1.48 in buffer and plasma, respectively. 5-MOP distribution in blood was simulated. The free fraction of 5-MOP in blood could be increased in hypoalbuminemia, unchanged in acute inflammation, and decreased by FFA.
Six oxicams, sudoxicam, isoxicam, piroxicam, tenoxicam, meloxicam and lornoxicam, were compared in an attempt to understand why, despite close chemical structures, two of them were associated with an increased risk of toxicity in patients. Different factors have been revealed which may explain these differences. A weak association constant to human serum albumin (HSA), together with a high plasma concentration, favours a rapid increase in unbound concentration (Cu) when total plasma concentration rises (peak of absorption). Pathological states may enhance this increase when both HSA plasma concentration is decreased and free fatty acid concentrations are increased. However, the main cause of toxicity may be the existence in some subjects of HSA natural mutants whose ability to bind oxicams is markedly lower than normal.