Distribution of chlorpromazine in a simplified blood influenced by various drugs

From hazard to risk prioritization: a case study to predict drug-induced cholestasis using physiologically based kinetic modeling

Cholestasis is characterized by hepatic accumulation of bile acids. Clinical manifestation of cholestasis only occurs in a small proportion of exposed individuals. The present study aims to develop a new approach methodology (NAM) to predict drug-induced cholestasis as a result of drug-induced hepatic bile acid efflux inhibition and the resulting bile acid accumulation. To this end, hepatic concentrations of a panel of drugs were predicted by a generic physiologically based kinetic (PBK) drug model. Their effects on hepatic bile acid efflux were incorporated in a PBK model for bile acids. The predicted bile acid accumulation was used as a measure for a drug's cholestatic potency. The selected drugs were known to inhibit hepatic bile acid efflux in an assay with primary suspension-cultured hepatocytes and classified as common, rare, or no for cholestasis incidence. Common cholestasis drugs included were atorvastatin, chlorpromazine, cyclosporine, glimepiride, ketoconazole, and ritonavir. The cholestasis incidence of the drugs appeared not to be adequately predicted by their Ki for inhibition of hepatic bile acid efflux, but rather by the AUC of the PBK model predicted internal hepatic drug concentration at therapeutic dose level above this Ki. People with slower drug clearance, a larger bile acid pool, reduced bile salt export pump (BSEP) abundance, or given higher than therapeutic dose levels were predicted to be at higher risk to develop drug-induced cholestasis. The results provide a proof-of-principle of using a PBK-based NAM for cholestasis risk prioritization as a result of transporter inhibition and identification of individual risk factors.

A protein-coated magnetic beads as a tool for the rapid drug-protein binding study

A simple and fast method for the determination of the association constant (K(a)) of ligand to human serum albumin (HSA) has been developed by using human serum albumin-coated magnetic beads (HSA-MB). To date, magnetic beads (MB) have been increasingly used as a bioseparation tool, especially for DNA, RNA, protein, enzyme and cell isolation or purification. In this study, HSA-MB were used as a new tool to determine the affinity of known ligands to HSA. The K(a) for l-tryptofan, fenoprofen, ketoprofen, tolbutamide and warfarin obtained from Schathard analysis are consistent with previously reported values. The different K(a) values for ketoprofen after the acetylation of HSA-MB by preincubation with acetylosalicylic acid indicate that these beads can be successfully adapted in combined experiment. In addition, the HSA-MB experiment with phenytoin and valproic acid proved to be a simple method to examine drug displacement effect.

Inhibitory effect of phenothiazines on the binding of [3H]perazine to alpha 1-acid glycoprotein

A system is described which allows the determination of the affinity constant of unlabelled drugs to alpha 1-acid glycoprotein (alpha 1-AGP) by displacing [3H]perazine from the binding protein with equilibrium dialysis. All drugs investigated appear to bind to only one site at the alpha 1-AGP molecule. From experiments, in which the chemical structure of the displacers was varied, the fragment 21-31 of the amino acid sequence appears to be a candidate for hydrophobic interactions. The glutamic acids 177 and 178 of the alpha 1-AGP molecule could be involved in ionic interactions with the side chain of phenothiazine derivatives. The relevance of alpha 1-AGP for drug binding, distribution, and the possible reasons for insufficient correlation between psychotropic plasma concentration and therapeutic response is discussed.

The distribution of chlorpromazine between plasma and erythrocytes

Chlorpromazine is found to be taken up by the erythrocytes in a dissociable binding similar to that of the plasma protein binding so that an equilibrium is attained between these binding sites. The plasma/cell ratio is on an average 2 but is subject to large interindividual variations. This ratio is only moderately influenced by the presence of other drugs and anticoagulants in the blood. The consequences of the cell binding of drugs for the analytical result when using plasma or whole blood and the evaluation of blood concentrations of their relation to the therapeutic effect are discussed.

[The influence of plasma protein binding on distribution and pharmacological activity of tranquilizers of the benzodiazepine group (author's transl)]

This paper discusses the problem if the plasma protein binding of benzodiazepine derivatives can influence distribution and pharmacological activity of the drugs. The distribution of the benzodiazepines in the organism is influenced not only by the plasma protein binding of the drugs, but also by several other factors, especially since the drugs are mostly lipophilic. Thus, an effect of the plasma protein binding on the distribution can only be expected if the benzodiazepine derivative is highly bound to the plasma proteins. Thus results have been shown only for diazepam and chlordiazepoxid, which indicate an effect of the plasma protein binding on distribution and pharmacological activity, for example the existence of a direct correlation between unwanted CNS depressions and low plasma albumin concentrations and a direct correlation between the plasma protein binding and the biological half-life. There are no observations available on a displacement of other drugs from their binding to plasma proteins by benzodiazepines. The observed displacement of thyroid hormones from their binding to plasma proteins seems to have only a significance for thyroid function tests in vitro. It was shown that benzodiazepines decrease the amount of L-tryptophan bound to serum albumin in vitro and in vivo and increased therewith the L-tryptophan concentration in the brain. At present it can not be confirmed if these observations bear any significance on the pharmacological activity of the drugs. But these experiments demonstrate the significance of the use of albumin as a model for the interaction of drugs with tissue or receptorproteins.

Spectroscopic studies on the complex formation of suramin with bovine and human serum albumin

The binding of suramin to bovine and human serum albumin was investigated by gel filtration and spectroscopic measurements. Besides some low-affinity binding sites suramin has, on the bovine serum albumin molecule one and on the human serum albumin molecule two, high-affinity binding sites. Spectroscopic measurements reveal that there are large differences between the albumins in the mechanism of binding to the high-affinity binding sites. Further, it is suggested that high concentrations of suramin provoke an unfolding of the albumin moleculse. In order to explain the unusual behaviour of suramin in connection with the displacement of other ligands from the albumin binding the fluorescence probe 1-anilino-8-naphthalenesulfonic acid (ANS) was employed as a reporter group molecule for fluorescence as well as circular dichroism measurements. By these measurements it could be shown that suramin greatly influences the microorganization of both albumin molecules. In the case of these measurements large differences between bovine and human serum albumin were also found.