Pharmacokinetics of chlorimipramine, chlorpromazine and their N-dealkylated metabolites in plasma of healthy volunteers after a single oral dose of the parent compounds

The Impact of the Antipsychotic Medication Chlorpromazine on Cytotoxicity through Ca2+ Signaling Pathway in Glial Cell Models

Chlorpromazine, an antipsychotic medication, is conventionally applied to cope with the psychotic disorder such as schizophrenia. In cellular studies, chlorpromazine exerts many different actions through calcium ion (Ca²⁺) signaling, but the underlying pathways are elusive. This study explored the effect of chlorpromazine on viability, Ca²⁺ signaling pathway and their relationship in glial cell models (GBM 8401 human glioblastoma cell line and Gibco® Human Astrocyte (GHA)). First, chlorpromazine between 10 and 40 μM induced cytotoxicity in GBM 8401 cells but not in GHA cells. Second, in terms of Ca²⁺ homeostasis, chlorpromazine (10-30 μM) increased intracellular Ca²⁺ concentrations ([Ca²⁺]_i) rises in GBM 8401 cells but not in GHA cells. Ca²⁺ removal reduced the signal by approximately 55%. Furthermore, chelation of cytosolic Ca²⁺ with BAPTA-AM reduced chlorpromazine (10-40 μM)-induced cytotoxicity in GBM 8401 cells. Third, in Ca²⁺-containing medium of GBM 8401 cells, chlorpromazine-induced Ca²⁺ entry was inhibited by the modulators of store-operated Ca²⁺ channel (2-APB and SKF96365). Lastly, in Ca²⁺-free medium of GBM 8401 cells, treatment with the endoplasmic reticulum Ca²⁺ pump inhibitor thapsigargin completely inhibited chlorpromazine-increased [Ca²⁺]_i rises. Conversely, treatment with chlorpromazine abolished thapsigargin-increased [Ca²⁺]_i rises. Inhibition of phospholipase C (PLC) with U73122 abolished chlorpromazine-increased [Ca²⁺]_i rises. Together, in GBM 8401 cells but not in GHA cells, chlorpromazine increased [Ca²⁺]_i rises by Ca²⁺ influx via store-operated Ca²⁺ entry and PLC-dependent Ca²⁺ release from the endoplasmic reticulum. Moreover, the Ca²⁺ chelator BAPTA-AM inhibited cytotoxicity in chlorpromazine-treated GBM 8401 cells. Therefore, Ca²⁺ signaling was involved in chlorpromazine-induced cytotoxicity in GBM 8401 cells.

Drug-induced cholestasis assay in primary hepatocytes

Drug-induced cholestasis (DIC) is a major cause of clinical failure of drug candidates. Numerous patients worldwide are affected when exposed to marketed drugs exhibiting a DIC signature. Prospective identification of DIC during early compound development remains challenging. Here we describe the optimized in vitro procedure for early assessment and prediction of an increased DIC risk. Our method is based on three principles:•Exposure of primary human hepatocyte cultures to test compounds in the absence and presence of a physiologically relevant mixture of endogenous bile salts.•Rapid and quantitative assessment of the influence of concomitant bile salt exposure on hepatocyte functionality and integrity after 24 h or 48 h of incubation.•Translation of the in vitro result, expressed as a DIC index (DICI) value, into an in vivo safety margin.Using our historical control data, a new (data driven) DICI cut-off value of 0.78 was established for discerning cholestatic and non-cholestatic compounds. Our DIC assay protocol was further improved by now relying on the principle of the no observable adverse effect level (NOAEL) for determining the highest test compound concentration corresponding to a DICI  ≥  0.78. Predicted safety margin values were subsequently calculated for compounds displaying hepatotoxic and/or cholestatic effects in patients, thus enabling evaluation of the performance of our DIC assay. Of note, this assay can be extended to explore the role of drug metabolites in precipitating DIC.

Atypical antipsychotics as noncompetitive inhibitors of alpha4beta2 and alpha7 neuronal nicotinic receptors

It has been suggested that the interaction of antipsychotic medications with neuronal nicotinic receptors may increase the cognitive dysfunction associated with schizophrenia and may explain why current therapies only partially address this core feature of the illness. In the present studies we compared the effects of the atypical antipsychotics quetiapine, clozapine and N-desmethylclozapine to those of the typical antipsychotics haloperidol and chlorpromazine on the alpha4beta2 and alpha7 nicotinic receptor subtypes. The binding of [(3)H]-nicotine to rat cortical alpha4beta2 receptors and [(3)H]-methyllycaconitine to rat hippocampal alpha7 receptors was not affected by any of the compounds tested. However, Rb(+) efflux evoked either by nicotine or the selective alpha4beta2 agonist TC-1827 from alpha4beta2 receptors expressed in SH-EP1 cells and nicotine-evoked [(3)H]-dopamine release from rat striatal synaptosomes were non-competitively inhibited by all of the antipsychotics. Similarly, alpha-bungarotoxin-sensitive epibatidine-evoked [(3)H]-norepinephrine release from rat hippocampal slices and acetylcholine-activated currents of alpha7 nicotinic receptors expressed in oocytes were inhibited by haloperidol, chlorpromazine, clozapine and N-desmethylclozapine. The inhibitory effects on nicotinic receptor function produced by the antipsychotics tested occurred at concentrations similar to plasma levels achieved in schizophrenia patients, suggesting that they may lead to clinically relevant effects on cognition.

Clomipramine induces the opening of Na+ channels in the frog skin epithelium

This paper studies the effect of clomipramine on the electrical parameters of the frog skin epithelium. We have found that clomipramine induces: 1) an increase in short circuit current that is equivalent to an increase in net Na+ flux, 2) an increase in total transepithelial conductance, 3) a depolarisation of the apical barrier, and 4) a decrease in the fractional resistance of the apical membrane. These results suggest that clomipramine promotes an increase in the sodium permeability of the apical barrier by increasing either the concentration of amiloride-sensitive Na+ channels or by increasing their individual conductance. Using kinetic models, values for the affinity constants for clomipramine and amiloride were estimated (K(Clo)=(18.l +/- l.04) x l0(-6) M; K(Amil) = 56 x 10(-8) M). Identical studies were performed for eel intestinal epithelium and no significant changes on the short circuit current were observed.

N-Dealkylation of chlorimipramine and chlorpromazine by rat liver microsomal cytochrome P450 isoenzymes

The role of different cytochrome P450 isozymes (CYP) in the N-demethylation of chlorimipramine and chlorpromazine has been investigated in liver microsomes from rats by studying the effects of multiple subchronic doses of chlorimipramine, chlorpromazine, phenobarbital and beta-naphthoflavone on the N-demethylation of ethylmorphine, mono-N-demethyl-chlorimipramine and chlorpromazine and on the hydroxylation of aniline. With control microsomes, CYP-dependent metabolism of chlorimipramine and chlorpromazine (100 nmol; 30 min incubation) resulted in the formation of predominantly chlorimipramine (46.5 +/- 4.9 nmol) whereas chlorpromazine (14.1 +/- 0.9 nmol) accounted for only part of the overall metabolism of chlorpromazine. Multiple doses of chlorimipramine increased the capacity of microsomes to N-demethylate ethylmorphine (9.8 +/- 0.73 and 6.08 +/- 0.06 nmol min(-1) (mg protein)(-1) for chlorimipramine-treated and control rats, respectively) as well as itself (4.65 +/- 0.25 and 3.10 +/- 0.33 nmol min(-1) (mg protein)(-1), respectively). Multiple doses of chlorpromazine induced aniline-hydroxylase activity (1.11 +/- 0.16 and 0.94 +/- 0.06 nmol min(-1) (mg protein)(-1) for chlorimipramine and control microsomes, respectively) but the capacity to N-demethylate itself was unchanged. Phenobarbital treatment induced ethylmorphine N-demethylation activity, but did not affect N-demethylation activity, towards chlorimipramine and chlorpromazine. In control microsomes the N-demethylation capacity of chlorimipramine or chlorpromazine (0.160 +/- 0.025 and 0.015 +/- 0.003 nmol min(-1) (mg protein)(-1), respectively) was one order of magnitude lower than that of chlorimipramine or chlorpromazine. The capacity to N-demethylate either chlorimipramine or chlorpromazine was increased by treatment with either phenobarbital or beta-naphthoflavone. In control microsomes, sulphaphenazole markedly inhibited both chlorimipramine-N-mono- and di-N-demethylation, whereas quinidine markedly inhibited the rate of formation of chlorpromazine. The CYP2C and CYP2D subfamilies seem to be involved in the mono N-demethylation of chlorimipramine and chlorpromazine, respectively. Moreover the CYP1A and CYP2B subfamilies might participate in the N-demethylation of either chlorimipramine or chlorpromazine. This could have important implications in the clinical use of chlorimipramine and chlorpromazine in view of the genetic polymorphism of CYP2C and CYP2D isozymes in man.

Rat tissue concentrations of chlorimipramine, chlorpromazine and their N-demethylated metabolites after a single oral dose of the parent compounds

A single oral dose of 90 mg kg-1 chlorimipramine or chlorpromazine, corresponding to 54.5 or 55.9 mumol, respectively, was given to male Sprague-Dawley rats and concentrations of parent drugs and their N-desmethyl metabolites measured by gas chromatography in plasma and major organs (brain, liver, lung, kidney, heart, spleen and peritoneal fat). In the case of chlorimipramine, N-desmethyl metabolite levels were consistently higher than those of the parent drug for the entire observation period of 24 h in all tissues except fat, while lower N-desmethyl metabolite/parent compound ratios were observed for chlorpromazine. N-Desmethyl metabolite kinetics of chlorimipramine appeared to be elimination-rate limited, while those of chlorpromazine were formation-rate limited. In all analysed organs, the maximu detectable drug+metabolite concentrations accounted for only 2.3 and 4.6% of the initial dose of chlorimipramine and chlorpromazine. Chlorpromazine treatment gave rise to an area under the total amount-time curve (AUC0-24) for parent drug+metabolites, 3.9-fold that for chlorimipraine. Closer scrutiny discloses a conversion ratio of parent compound to N-desmethyl metabolite of 1.1 for chlorpromazine and of 2.2 for chlorimipramine, indicating the greater efficiency of chlorimipramine metabolism in all compartments. The expected high conversion index found in the liver (2.3) reaches its maximum of 5.4 in the lung. Fractional data analysis of chlorimipramine and chlorpromazine distribution patterns revealed greater organ transfer for the N-desmethyl metabolites than for the more stably-located parent compounds. The N-desmethyl metabolites of chlorimipramine apparently moved from liver to lung, kidney and spleen, whereas N-desmethylchlopromazine moved preferentially to the brain and lung tissue. This single dose study of chlorimipramine and chlorpromazine kinetics, highlights the two distinct dispositional processes at work in the rat in all likelihood, attributable to different absorption patterns, to a slower metabolism and, thus, to the longer persistence of chlorpromazine.