Propranolol Binding Research Articles

Altered Drug–Serum Protein Binding in the Genetically Obese Zucker Rat

Drug–serum protein binding was evaluated in genetically obese Zucker rats, their lean littermates, and lean Sprague–Dawley rats. The free fraction (fp) of phenytoin was significantly higher in the obese rat (fp=0.177) compared to its lean littermate (fp=0.136), apparently due to displacement by free fatty acids. Conversely, diazepam and propranolol fp values were decreased in the obese Zucker rat (fp=0.107 and fp=0.122, respectively) compared to the lean Zucker rat (fp=0.140 and fp=0.174, respectively). Evidence strongly suggests that the increased binding of propranolol was not due to elevations in the serum concentrations of α1-acid glycoprotein (as is the case in the human obese population). Rather, the decreased fp for both diazepam and propranolol was a result of increased lipoprotein partitioning. Strain differences between the lean Zucker rat and lean Sprague–Dawley rat were also evident, with the serum binding of the Sprague–Dawley rat more closely resembling the obese Zucker rat.

Modification of propranolol binding to alpha-1-acid glycoprotein by serum albumin

Modification of propranolol binding to alpha-1-acid glycoprotein by serum albumin

Effect of the Sialylation State of α1-Acid Glycoprotein on Propranolol Binding

α1-Acid glycoprotein (AAG) exists in a variety of sialylated states which can be influenced by certain disease states. The purpose of the present study was to establish the effect of the sialylation state of AAG on the binding of a model cationic drug (propranolol). Extensive in vitro enzymatic desialylation of isolated human AAG was achieved utilizing neuraminidase bonded to agarose beads. Propranolol binding to native and desialylated AAG was determined by equilibrium dialysis. Desialylated AAG exhibited a modest increase in propranolol free fraction due to a decrease in the affinity constant (Ka) compared to untreated AAG (3.3 × 105 M−1 versus 4.0 × 105 M−1, respectively). A modest 15% increase was predicted for the free fraction of propranolol in serum containing desialylated AAG at therapeutic propranolol concentrations (<0.1 μg/ml). Therefore, the clinical significance of desialylated AAG appears to be minor with respect to propranolol binding.

Effect of Late Pregnancy on Salicylate, Diazepam, Warfarin, and Propranolol Binding

Effect of Late Pregnancy on Salicylate, Diazepam, Warfarin, and Propranolol Binding

Drug binding in the undernourished: a study of the binding of propranolol to alpha 1-acid glycoprotein.

The binding of propranolol, a drug commonly used in cardiovascular disorders, to alpha 1-acid glycoprotein (AGP) was studied in vitro in malnutrition. Compared to normal and hospital controls, the level of AGP was found to be elevated in undernourished subjects with and without infection. In the same patients the free drug percentage was significantly diminished. A significant inverse relationship was observed between the percentage of free drug and the level of AGP. The finding suggests that there may be need for an altered dosage regimen in the undernourished.

Effect of Late Pregnancy on Salicylate, Diazepam, Warfarin, and Propranolol Binding

Serum protein binding was measured in six women 38 wk pregnant and in five control subjects. Three distinct binding sites for drugs on human serum albumin have been identified. To determine whether changes in binding during pregnancy occur for common drugs or only for drugs that bind to a specific binding site, serum protein binding of three drugs—diazepam (site I), warfarin (site III), and salicylate—and four fluorescent probes—dansylsarcosine (site I), l-anilino-8-naphthalenesulfonate (site I), 7-anilinocoumarin-4-acetic acid (site II), and 5-dimethylaminonaphthalene-1-sulfonamide (DNSA) (site III)—were determined in control and pregnant sera. Unbound fractions of diazepam and salicylate in pregnant women increased but the unbound fraction of warfarin did not change. Dissociation constants (Kd1) of all fluorescent probes but DNSA were almost the same in control and pregnant sera, while the Kd1 of DNSA in pregnant serum was approximately 50% of control. Binding capacities of all probes decreased, which was attributed to decreased serum albumin concentration. We concluded that serum protein binding of drugs that bind to site I or site II on albumin decreased largely because of the reduced serum albumin concentration during pregnancy and that the binding of drugs that bind to site III changed little because of compensating effects of the decrease in serum albumin concentration and the increase in binding affinity to serum albumin. Serum concentration of α1-acid glycoprotein and serum binding of propranolol did not change in pregnant women. Clinical Pharmacology and Therapeutics (1984) 36, 201–208; doi:10.1038/clpt.1984.163

Serum protein binding and the role of increased alpha 1‐acid glycoprotein in moderately obese male subjects.

Serum protein and lipid concentrations as well as the serum protein binding of propranolol, diazepam and phenytoin were measured in normal weight and obese volunteers. Concentrations of alpha 1-acid glycoprotein (AAG) in the obese subjects were double that of the lean controls. Conversely, concentrations of high density lipoproteins (HDL) were decreased in the obese group. The serum binding of propranolol was increased in the obese subjects and correlated with serum AAG concentrations. Diazepam binding was slightly decreased in the obese as a result of lower serum albumin concentrations and elevated free fatty acids. The binding of phenytoin was comparable in all of the volunteers. These findings point out some of the complex pathophysiologic changes associated with obesity which may in turn influence drug disposition and hence drug therapy in the obese patient.

Alpha 1-acid glycoprotein concentrations and propranolol binding in elderly patients with acute illness.

Alpha 1-acid glycoprotein (AAG) concentrations and propranolol binding were investigated in the serum of elderly hospitalized patients with acute illness, and healthy elderly and young subjects. Significantly greater AAG concentrations and reduced unbound propranolol fraction were observed in the elderly with acute disease compared to the elderly controls. The greatest changes (up to five-fold) occurred with cancer, with lesser changes associated with myocardial infarction and ischaemic heart disease, acute infection, heart failure, chronic obstructive respiratory disease, and cerebrovascular accident. Various miscellaneous conditions were also associated with high AAG concentrations and enhanced propranolol binding. The healthy elderly had higher AAG concentrations and lower unbound propranolol fractions than the healthy young group. Overall there was a highly significant correlation between the propranolol binding ratio (bound/free) and the serum AAG concentration. These results suggest that the elderly population may be particularly susceptible to changes in AAG concentrations, and that during acute illness interpretation of serum concentrations of drugs which bind mainly to AAG, may require knowledge of their free fractions.

A method for the assay of α 1-acid glycoprotein in dog serum and its application to the plasma binding of propranolol and oxprenolol in animals receiving rifampicin

A method for determination of α 1-acid glycoprotein (α 1-AGP) in dog serum was developed. Dog α 1-AGP was purified to homogeneity from pooled serum by DEAE and CM ion exchange chromatography. A monospecific antibody was obtained by injecting the antigen in rabbits. The antibody was used in a turbidimetric method that allowed detection at 10 μg/ml in serum. A linear correlation was found between the optical density and α 1-AGP concentration up to 20 μg α 1-AGP in the sample. The method has been used to demonstrate the effect of treatment with rifampicin on the α 1-AGP serum concentrations and its relation to the protein binding of oxprenolol and propranolol.

Effect of late pregnancy on salicylate, diazepam, warfarin, and propranolol binding: use of fluorescent probes.

Serum protein binding was measured in six women 38 wk pregnant and in five control subjects. Three distinct binding sites for drugs on human serum albumin have been identified. To determine whether changes in binding during pregnancy occur for common drugs or only for drugs that bind to a specific binding site, serum protein binding of three drugs--diazepam (site I), warfarin (site III), and salicylate--and four fluorescent probes--dansylsarcosine (site I), 1-anilino-8-naphthalenesulfonate (site I), 7-anilinocoumarin-4-acetic acid (site II), and 5-dimethylaminonaphthalene-1-sulfonamide (DNSA) (site III)--were determined in control and pregnant sera. Unbound fractions of diazepam and salicylate in pregnant women increased but the unbound fraction of warfarin did not change. Dissociation constants (Kd1) of all fluorescent probes but DNSA were almost the same in control and pregnant sera, while the Kd1 of DNSA in pregnant serum was approximately 50% of control. Binding capacities of all probes decreased, which was attributed to decreased serum albumin concentration. We concluded that serum protein binding of drugs that bind to site I or site II on albumin decreased largely because of the reduced serum albumin concentration during pregnancy and that the binding of drugs that bind to site III changed little because of compensating effects of the decrease in serum albumin concentration and the increase in binding affinity to serum albumin. Serum concentration of alpha 1-acid glycoprotein and serum binding of propranolol did not change in pregnant women.

Binding of oxprenolol and propranolol to serum, albumin and α1-acid glycoprotein in man and other species

Species differences in binding of basic drugs have only occasionally been studied and we have therefore measured the binding of the β-adrenergic blockers oxprenolol and propranolol in (1) serum of healthy humans, dogs, rats and rabbits and of rabbits with experimental arthritis, (2) a solution of albumin of these species and (3) a solution of human α 1-AGP. In humans, dogs, rats and arthritic rabbits, binding of oxprenolol and propranolol was much higher in serum than in albumin solution; in healthy rabbits serum binding was very low and not different from albumin binding. For both drugs, concentration-dependency was seen in serum of dogs, humans and rats and of arthritic rabbits; a similar concentration-dependency was found for human α 1-AGP solution, but not for human albumin and for serum of healthy rabbits. Tris (2-butoxyethyl)-phosphate (TBEP), a known displacer of drugs from α 1-AGP in humans, decreased binding in serum of all species except the rabbit. For both β-blockers, species differences in capacity constants were found; species differences in affinity constants were present only for propranolol. These results suggest that in humans, dog and rat, but much less in rabbits, oxprenolol and propranolol bind mainly to α 1-AGP and that binding to α 1-AGP is more important for oxprenolol than for propranolol.

Effects of chlorpromazine on the disposition and beta-adrenergic blocking activity of propranolol in the dog.

The effects of chlorpromazine (100 mg p.o., 2 hr before propranolol) on the disposition and beta-adrenergic blocking actions of both intravenous (6 mg) and oral (40 mg) propranolol were studied in the dog. Chlorpromazine pretreatment significantly reduced (69%) the oral clearance of propranolol, resulting in significant increases in propranolol bioavailability (159%), and in the total beta-adrenergic blocking activity (111%) after the oral dose. The increase in the total beta-adrenergic blocking activity of oral propranolol after chlorpromazine pretreatment was mostly due to an increased contribution from the parent compound; the apparent activity from active propranolol metabolites was not affected by chlorpromazine. Chlorpromazine pretreatment had no significant influence on the systemic clearance, elimination half-life, apparent volume of distribution, and plasma binding of propranolol, or on the apparent hepatic blood flow. After intravenous propranolol, chlorpromazine pretreatment had no effect on either the total amount of beta-adrenergic blocking activity or the amount of activity attributable to active metabolites. The decreased oral propranolol clearance by chlorpromazine was seen as a shift to the left in the propranolol dose vs. AUC relationship, eliminating the apparent nonlinear kinetic behavior of oral propranolol, and reducing the apparent oral threshold dose. Chlorpromazine's major, if not only, effect on propranolol disposition was to reduce the presystemic elimination of propranolol, possibly through inhibition of its metabolism via a pathway other than ring oxidation.

DISPLACEMENT OF SOME BASIC DRUGS FROM HUMAN SERUM PROTEINS BY ENFLURANE, HALOTHANE AND THEIR MAJOR METABOLITES

The influence of volatile anaesthetics (halothane, enflurane) on the serum protein binding of three highly bound basic drugs has been studied in vitro by equilibrium dialysis. Radioactive labelled isotopes were used for the determination of drug concentrations. Enflurane, halothane and the halothane metabolite trifluoroacetic acid (TFA) inhibited the binding of diazepam to serum and to its main binding protein, albumin. The binding of diazepam to albumin was inhibited in a competitive manner and was not related to the anaesthetic potency of the vapours. Thus the observed displacement of diazepam should be regarded as a side-effect of the volatile anaesthetics. The binding of propranolol and prazosin in serum was not significantly influenced by the investigated anaesthetics. At clinically relevant concentrations of the anaesthetics, diazepam was displaced significantly only by enflurane with an increase in free fraction of 60% in serum. TFA in concentrations seen after operation significantly increased the free fraction of diazepam up to 90%. We conclude that enflurane anaesthesia may temporarily potentiate the pharmacological effect of diazepam and that, in the postoperative period following halothane anaesthesia, a more rapid elimination of diazepam could be expected.

Quinidine and propranolol binding to very low and low density lipoproteins of human plasma.

The interaction of quinidine (Q) and propranolol (P) with human very low density lipoproteins (VLDL) and low density lipoproteins (LDL) was determined by ultrafiltration in phosphate buffer (pH 7.4) for Q and in phosphate and Tris buffers (pH 7.4-7.5) for P, respectively. The Scatchard plots of Q are curved and were best described by a model assuming two independent classes of binding sites on lipoproteins. When working with P, the Scatchard plots were also nonlinear, but positive cooperativity was observed for the VLDL fraction in phosphate buffer and apparently also for the LDL fraction in Tris buffer. These nonlinear curves were described by the model used for Q, excluding any data falling in the cooperating region. The binding parameters, primary (K1) and secondary (K2) affinity constants and the number of sites in each class of independent binding sites, were generated by a computer program. The results of this in vitro study suggest that drug binding (and possibly distribution) to lipoproteins may be affected by the nature and concentration of some ions present in serum.

Influence of age on serum protein binding of propranolol.

The extent of propranolol protein binding was determined in three different age groups of healthy drug-free caucasian males. Volunteers selected for study were 6-15 years old, 25-36 years old and 68-76 years old. Ten milliliters of blood were obtained via venipuncture and collected in glass tubes from the subjects after an overnight fast. Binding determinations were performed by equilibrium dialysis using radiolabelled propranolol. Serum albumin and alpha 1-acid glycoprotein concentrations were determined in all subjects by radial immunodiffusion. The results obtained showed wide intersubject variability in the binding ratio of propranolol and serum concentrations of alpha 1-acid glycoprotein. Mean albumin serum concentration was found to be significantly lower in the elderly group as compared to the adult and pediatric groups (p less than 0.02). A positive correlation was found between the binding ratio of propranolol and the serum concentration of alpha 1-acid glycoprotein in all the subjects (r = + 0.66, p less than 0.005). No significant correlation was found between the binding ratio of propranolol and the serum concentration of albumin (r = -0.03, p less than 0.88). These data suggest that the extent of propranolol binding is influenced primarily by serum concentrations of alpha 1-acid glycoprotein and not by differences in age.

Increased availability of propranolol in rats with uranyl nitrate-induced acute renal failure.

The effect of acute renal failure (ARF) on the pharmacokinetics of propranolol was investigated. The model of ARF was produced by the subcutaneous injection of uranyl nitrate to rats (10 mg/kg) and was used 3 d after treatment. Uranyl nitrate-treated rats showed significantly higher plasma concentrations of propranolol after oral administration and the area under the plasma concentration-time curve increased about 3-fold compared to control rats. The plasma disappearance of propranolol after intravenous administration did not differ significantly between control and ARF. The mean availability of propranolol after oral administration increased from 0.120 in control to 0.215 in ARF (p less than 0.005). Absorption of propranolol was almost complete and no significant difference was found between two groups. No changes in plasma protein binding of propranolol and hepatic blood flow were observed in ARF. On the other hand, hepatic clearance of propranolol determined by liver perfusion studies showed a significant reduction in ARF and the calculated intrinsic clearance of unbound propranolol at a dose of 6.25 mg was 26.8 +/- 2.3 ml/min in control and 16.0 +/- 2.3 ml/min in ARF (p less than 0.01). These results demonstrate that the oral availability of propranolol increased in ARF due to a reduction in the hepatic presystemic elimination as compared to healthy control rats.

Stereoselective binding of propranolol to human plasma, alpha 1-acid glycoprotein, and albumin.

Our aim was to determine possible stereoselectivity in the plasma binding of propranolol. Equilibrium dialysis with plasma from seven healthy subjects and a deuterium-labeled pseudoracemate of propranolol was used. Plasma binding of the propranolol enantiomers differed with the unbound fraction of (-)-propranolol (22 +/- 2%; mean +/- SE) being smaller than that of (+)-propranolol (25.3 +/- 1.9%). The (-)/(+)-propranolol ratio for the unbound fraction, a measure of the stereoselectivity, was 0.86 +/- 0.02. There was an inverse correlation between the unbound (-)/(+)-propranolol ratio in individual subjects and overall binding of (+/-)-propranolol, indicating greater stereoselectivity at higher total binding. To assess the site of the stereoselective binding to plasma proteins, the binding of (+)- and (-)-propranolol to human alpha 1-acid glycoprotein (AGP) and human serum albumin (HSA) was examined. The binding to AGP was stereoselective for (-)-propranolol with a (-)/(+)-propranolol ratio for the unbound fraction of 0.79 +/- 0.01, whereas (+)-propranolol was bound to a greater extent to HSA with a (-)/(+)-propranolol ratio for the unbound fraction of 1.07 +/- 0.01. Although these results demonstrate opposite stereoselectivity in the binding of (+)- and (-)-propranolol to AGP and HSA, the stereoselective binding of (-)-propranolol to AGP predominates in plasma. This stereoselective plasma binding of the (-)-enantiomer of propranolol could limit the access of this more active enantiomer to beta-receptors or other active sites. The uptake of propranolol by red blood cells was not stereoselective.

Serum alpha 1-acid glycoprotein and the binding of drugs in obesity.

Although clinically relevant, drug-protein interactions in the morbidly obese population have not been studied thoroughly. The objective of this study was to evaluate serum chemistry profiles and the degree of serum protein binding of propranolol, diazepam and phenytoin in the serum of four female, morbidly obese (greater than 190% of ideal body weight) and eight control female subjects. Serum triglyceride concentrations were higher and high-density lipoproteins were lower in the obese subjects than in the control group. Serum albumin and total protein concentrations in the obese were not different from controls. Unexpectedly, alpha 1-acid glycoprotein concentrations were doubled in the obese subjects (mean obese value 121 mg/100 ml vs 62.9 mg/100 ml for the control subjects). Obese subjects had a mean fraction unbound (fu) for propranolol of 0.086, which was significantly different from the controls (fu = 0.123). The binding of diazepam was decreased slightly in the obese subjects. The binding of phenytoin was similar in both groups. The altered serum chemistry of obesity may play a significant role in the drug management of the obese patient by altering drug-protein interactions.

Binding of propranolol and iodocyanopindolol to isolated cells, homogenates and plasma membranes of rat liver, lung, kidney and heart

3H-(±) propranolol and 125I-(±) cyanopindolol have been used to characterize β adrenoceptors of liver, lung, kidney and heart of rat. Two main binding parameters, K D and B max were measured using either cells, homogenates or plasma membranes of each organ (except heart). Results show that the most accurate determination of K D and B max involves: (1) a previous extraction of plasma membranes (2) the use of a ligand of a high affinity for β adrenoceptors (3) a high specific radioactivity of this ligand. 125I-(±) cyanopindolol seems to be a better ligand than 3H(±) propranolol for such determinations.

Pharmacokinetic drug interactions with propranolol

Propranolol is widely used in clinical practice and is frequently administered along with other drugs. The co-administration of propranolol and other drugs may result in either propranolol-induced changes in the disposition of other drugs or in effects of the other drugs on the pharmacokinetics of propranolol. These changes may be due to alteration in absorption, metabolism or to haemodynamic effects such as altered liver blood flow. Understanding the pharmacokinetics of propranolol is important to the rational interpretation of the effects of other drugs on propranolol's disposition. The absorption, protein binding and metabolism of propranolol may all be affected by the co-administration of other drugs. Induction of propranolol's metabolism by halofenate, phenytoin, phenobarbitone, rifampicin and alcohol have all been implicated in altering propranolol clearance, while inhibition of hepatic drug metabolising enzymes by chlorpromazine and cimetidine appear to reduce propranolol clearance. Propranolol may also affect the metabolism of other drugs such as antipyrine, chlorpromazine, theophylline and thyroid hormones. Suggestions that propranolol may alter quinidine's elimination have not been substantiated. By reducing liver blood flow propranolol may reduce the systemic clearance of other high extraction drugs such as lignocaine.