Levels of chlorpromazine and its active metabolites in rat brain and the relationship to central monoamine metabolism and prolactin secretion

Antihistamines, phenothiazine-based antipsychotics, and tricyclic antidepressants potently activate pharmacologically relevant human carbonic anhydrase isoforms II and VII

Carbonic anhydrases (CAs) are important regulators of pH homeostasis and participate in many physiological and pathological processes. CA activators (CAAs) are becoming increasingly important in the biomedical field since enhancing CA activity may have beneficial effects at neurological level. Here, we investigate selected antihistamines, phenothiazine-based antipsychotics, and tricyclic antidepressants (TCAs) as potential activators of human CAs I, II, IV, and VII. Our findings indicate that these compounds are more effective at activating hCA II and VII compared to hCA I and IV. Overall, hCA VII was the most efficiently activated isoform, particularly by phenothiazines and TCAs. This is especially relevant since hCA VII is the most abundant isoform in the central nervous system (CNS) and is implicated in neuronal signalling and bicarbonate balance regulation. This study offers additional insights into the pharmacological profiles of clinically employed drugs and sets the ground for the development of novel optimised CAAs.

Chlorpromazine, an Inverse Agonist of D1R-Like, Differentially Targets Voltage-Gated Calcium Channel (CaV) Subtypes in mPFC Neurons

The dopamine receptor type 1 (D1R) and the dopamine receptor type 5 (D5R), which are often grouped as D1R-like due to their sequence and signaling similarities, exhibit high levels of constitutive activity. The molecular basis for this agonist-independent activation has been well characterized through biochemical and mutagenesis in vitro studies. In this regard, it was reported that many antipsychotic drugs act as inverse agonists of D1R-like constitutive activity. On the other hand, D1R is highly expressed in the medial prefrontal cortex (mPFC), a brain area with important functions such as working memory. Here, we studied the impact of D1R-like constitutive activity and chlorpromazine (CPZ), an antipsychotic drug and D1R-like inverse agonist, on various neuronal Ca_V conductances, and we explored its effect on calcium-dependent neuronal functions in the mouse medial mPFC. Using ex vivo brain slices containing the mPFC and transfected HEK293T cells, we found that CPZ reduces Ca_V2.2 currents by occluding D1R-like constitutive activity, in agreement with a mechanism previously reported by our lab, whereas CPZ directly inhibits Ca_V1 currents in a D1R-like activity independent manner. In contrast, CPZ and D1R constitutive activity did not affect Ca_V2.1, Ca_V2.3, or Ca_V3 currents. Finally, we found that CPZ reduces excitatory postsynaptic responses in mPFC neurons. Our results contribute to understanding CPZ molecular targets in neurons and describe a novel physiological consequence of CPZ non-canonical action as a D1R-like inverse agonist in the mouse brain.

Classics in Chemical Neuroscience: Chlorpromazine

The discovery of chlorpromazine in the early 1950s revolutionized the clinical treatment of schizophrenia, galvanized the development of psychopharmacology, and standardized protocols used for testing the clinical efficacy of antipsychotics. Furthermore, chlorpromazine expanded our understanding of the role of chemical messaging in neurotransmission and reduced the stigma associated with mental illness, facilitating deinstitutionalization in the 1960s and 1970s. In this review, we will discuss the synthesis, manufacturing, metabolism and pharmacokinetics, pharmacology, structure-activity relationship, and adverse effects of chlorpromazine. In conclusion, we summarize the history and significant contributions of chlorpromazine that have resulted in this potent first-generation antipsychotic maintaining its clinical relevance for nearly 70 years.

Effects of phenothiazine-class antipsychotics on the function of α7-nicotinic acetylcholine receptors

The effects of phenothiazine-class antipsychotics (chlorpromazine, fluphenazine, phenothiazine, promazine, thioridazine, and triflupromazine) upon the function of the cloned α₇ subunit of the human nicotinic acetylcholine receptor expressed in Xenopus oocytes were tested using the two-electrode voltage-clamp technique. Fluphenazine, thioridazine, triflupromazine, chlorpromazine, and promazine reversibly inhibited acetylcholine (100 μM)-induced currents with IC₅₀ values of 3.8; 5.8; 6.1; 10.6 and 18.3 μM, respectively. Unsubstituted phenothiazine did not have a significant effect up to a concentration of 30 μM. Inhibition was further characterized using fluphenazine, the strongest inhibitor. The effect of fluphenazine was not dependent on the membrane potential. Fluphenazine (10 μM) did not affect the activity of endogenous Ca²⁺-dependent Cl⁻ channels, since the extent of inhibition by fluphenazine was unaltered by intracellular injection of the Ca²⁺ chelator BAPTA and perfusion with Ca²⁺-free bathing solution containing 2 mM Ba²⁺. Inhibition by fluphenazine, but not by chlorpromazine was reversed by increasing acetylcholine concentrations. Furthermore, specific binding of [¹²⁵I] α-bungarotoxin, a radioligand selective for α₇-nicotinic acetylcholine receptor, was inhibited by fluphenazine (10 μM), but not by chlorpromazine in oocyte membranes. In hippocampal slices, epibatidine-evoked [³H] norepinephrine release was also inhibited by fluphenazine (10 μM) and chlorpromazine (10 μM). Our results indicate that phenothiazine-class typical antipsychotics inhibit, with varying potencies, the function of α₇-nicotinic acetylcholine receptor.

Antipsychotics inhibit TREK but not TRAAK channels

Schizophrenia is a chronic mental illness affecting 0.4% of the population. Existing antipsychotic drugs are mainly used to treat positive symptoms such as hallucinations but have only poor effects on negative symptoms such as cognitive deficits or depression. TREK and TRAAK channels are two P domain background potassium channels activated by polyunsaturated fatty acids and mechanical stress. TREK but not TRAAK channels are regulated by Gs- and Gq-coupled pathways. The inactivation of the TREK-1 but not the TRAAK channel in mice results in a depression-resistant phenotype. In addition, it has been shown that antidepressants such as fluoxetine or paroxetine directly inhibit TREK channel activity. Here we show that different antipsychotic drugs directly inhibit TREK currents with IC(50) values of approximately 1 to approximately 20 microM. No effect is seen on TRAAK channel activity. We conclude that TREK channels might be involved in the therapeutic action of antipsychotics or in their secondary effects. Furthermore, TREK channels could play a role in the pathophysiology of psychiatric disorders such as depression and schizophrenia.

Biotransformation of chlorpromazine and methdilazine by Cunninghamella elegans

When tested as a microbial model for mammalian drug metabolism, the filamentous fungus Cunninghamella elegans metabolized chlorpromazine and methdilazine within 72 h. The metabolites were extracted by chloroform, separated by high-performance liquid chromatography, and characterized by proton nuclear magnetic resonance, mass, and UV spectroscopic analyses. The major metabolites of chlorpromazine were chlorpromazine sulfoxide (36%), N-desmethylchlorpromazine (11%), N-desmethyl-7-hydroxychlorpromazine (6%), 7-hydroxychlorpromazine sulfoxide (36%), N-hydroxychlorpromazine (11%), 7-hydroxychlorpromazine sulfoxide (5%), and chlorpromazine N-oxide (2%), all of which have been found in animal studies. The major metabolites of methdilazine were 3-hydroxymethdilazine (3%). (18)O(2) labeling experiments indicated that the oxygen atoms in methdilazine sulfoxide, methdilazine N-oxide, and 3-hydroxymethdilazine were all derived from molecular oxygen. The production of methdilazine sulfoxide and 3-hydroxymethdilazine was inhibited by the cytochrome P-450 inhibitors metyrapone and proadifen. An enzyme activity for the sulfoxidation of methdilazine was found in microsomal preparations of C. elegans. These experiments suggest that the sulfoxidation and hydroxylation of methdilazine and chlorpromazine by C. elegans are catalyzed by cytochrome P-450.

The metabolism of chlorpromazine N-oxide in man and dog

1. The metabolism of chlorpromazine N-oxide was studied in female dogs and adult male humans after a single oral dose. 2. There was extensive metabolism in both species in that between four and seven metabolites were separately identified in urine and faeces. Apart from chlorpromazine N-oxide, chlorpromazine N,S-dioxide was the only isolated metabolite which retained the N-oxide group. The other identified metabolites were chlorpromazine and its 7-hydroxy, sulphoxide, N-desmethyl, 7-hydroxy-N-desmethyl and N-desmethylsulphoxide derivatives. 3. With dog samples, metabolites were separated by h.p.l.c. and individually collected prior to mass spectrometric analysis. With human samples, metabolites were directly subjected to h.p.l.c.-mass spectrometric determination. With all metabolites their structures were confirmed by direct comparison of their mass spectra and chromatographic behaviours with those of authentic samples. 4. The metabolites identified in urine and faeces were for the most part the same in both species, with the exceptions that chlorpromazine N-oxide was identified in the faeces of dog only and 7-hydroxy-N-desmethylchlorpromazine was identified in the urine of man only. 5. The observation of N-oxide compounds in the excreta of both man and dog contrasted with that for the previously studied rat, where no such compounds were detected.

The metabolism of chlorpromazine N-oxide in the rat

1. The metabolism of chlorpromazine N-oxide was studied in female rats after a 20 mg/kg single oral dose. 2. Metabolites identified in both urine and faeces were chlorpromazine, 7-hydroxychlorpromazine, chlorpromazine sulphoxide, N-desmethylchlorpromazine and N-desmethylchlorpromazine sulphoxide. 3. Metabolites were separated by h.p.l.c. or g.l.c. prior to mass spectrometric analysis. The structures of the metabolites were confirmed by direct comparison of their mass spectra and chromatographic behaviours with those of authentic compounds. 4. Chlorpromazine N-oxide and any metabolite which retained the intact N-oxide function, such as chlorpromazine, N,S-dioxide, could not be identified in any of the extracts. 5. When 3H-chlorpromazine N-oxide was administered under the same conditions; approximately twice as much radioactivity was excreted in the faeces (52.1 +/- 9.7%) as in the urine (26.9 +/- 7.2%).

Radioimmunoassay for the N-oxide metabolite of chlorpromazine in human plasma and its application to a pharmacokinetic study in healthy humans

Antibodies specific to chlorpromazine N-oxide (CPZNO) were produced in rabbits immunized with a hapten-bovine serum albumin conjugate, which was prepared by linking the 7-position of the phenothiazine ring of the metabolite to the protein via a 4-carbon bridge. An extraction radioimmunoassay (RIA) was developed using this antiserum and shown to have adequate sensitivity and specificity for determination of plasma concentrations of CPZNO in the presence of chlorpromazine (CPZ) and its major metabolites. It was used together with the previously developed RIAs for CPZ, chlorpromazine sulfoxide (CPZSO), and 7-hydroxychlorpromazine (7-OHCPZ) to study the pharmacokinetics of CPZ and these metabolites in five healthy volunteers after they received a single 50-mg oral dose of CPZ. It is interesting to note that peak plasma concentrations of CPZNO were considerably higher than CPZ, and the apparent elimination half-lives of this metabolite were shorter than those of CPZ.

Nuclear magnetic resonance analysis of methotrimeprazine (levomepromazine) hydroxylation in humans

Two monohydroxylated metabolites of methotrimeprazine (levomepromazine), which previously have been identified in plasma and urine from psychiatric patients, were synthesized by nonenzymatic, FeCl2-catalyzed oxidation, isolated, and purified by preparative reversed-phase HPLC. Mass spectrometric analysis gave identical spectra for the two compounds, but did not reveal the positions of the OH groups. However, 1H NMR spectroscopy at 200 MHz demonstrated that one of the compounds, which had the shortest GC retention time on an OV-17 column, was hydroxylated in the 3-position on the phenothiazine nucleus, and that the other derivative was hydroxylated in the 7-position. The metabolism of methotrimeprazine differs, therefore, from that of its congener chlorpromazine, which is hydroxylated mainly in the 7-position in humans.

Blood to brain distribution of neuroleptics

Knowledge of the tissue distribution of drugs is important in interpreting other more commonly measured pharmacokinetic parameters, such as levels of drug in blood. For the neuroleptics, studies of blood to brain distribution are few and, due to technical differences between studies, the results are neither consistent within drugs nor comparable between drugs. We estimated the plasma to brain distribution of several common neuroleptics in rats using a single technique, the radioreceptor assay for neuroleptics. At doses that led to plasma levels similar to those achieved in clinical use, brain to plasma ratios ranged from 34 and 22 for fluphenazine and haloperidol, respectively, to 2.2 and 0.97 for thioridazine and mesoridazine, respectively. In general, clinical milligram potency and the favorability of distribution to brain ranked in the same order. These results may explain why such low levels of the high potency neuroleptics and such high levels of the low potency neuroleptics, greater than can be explained by relative differences between the same drugs in potency in vitro, are observed in blood both by radioreceptor and chemical assay techniques.

Behavioral interaction of adenosine and trifluoperazine in mice

Mice were implanted with chronic indwelling cannulae in the lateral cerebral ventricle. A dose-response curve was established for the effect of i.p. injections of trifluoperazine (TFP) on spontaneous locomotor activity. In addition, the behavioral interaction of i.p. injections of TFP with intracerebroventricular (i.c.v.) injections of adenosine (ADO) was examined. TFP depressed locomotor activity in a dose-dependent manner. A dose of ADO, which had no effect on locomotor activity when given alone, enhanced the depressant effects of TFP at all doses. As a control for the specificity of this behavioral interaction, mice also were given i.p. injections of TFP in combination with i.c.v. injections of 5'-N-ethylcarboxamidoadenosine (NECA), an uptake-resistant adenosine analogue. TFP and NECA did not interact to produce a significantly more pronounced locomotor depression. These results substantiate the notion that the sedative actions of TFP involve the inhibition of adenosine uptake and thus potentiation of extracellular adenosine levels.

Chlorpromazine and trifluoperazine potentiate the action of adenosine on rat cerebral cortical neurons

The effect of chlorpromazine and trifluoperazine on adenosine-evoked depressions of the spontaneous firing of rat cerebral cortical neurons has been studied. When applied by iontophoresis from multiple barrelled micropipettes, in amounts that did not affect neuronal firing rates, both substances enhanced the depressant actions of adenosine. Trifluoperazine did not enhance the depressant actions of the uptake resistant analog, adenosine 5'-N-ethylcarboxamide. Intravenously administered chlorpromazine and trifluoperazine (1 mg/kg) enhanced the depressant actions of iontophoretically applied adenosine. Caffeine antagonized the depressant effect on the firing of cortical neurons observed with larger applications of trifluoperazine. These findings support the conclusion, drawn from previous studies on the effects of phenothiazines on the uptake of adenosine by brain synaptosomes, that inhibition of adenosine uptake and potentiation of the actions of endogenously released adenosine may be a significant factor in the generation of the central actions of the phenothiazines.

Subnanogram quantitation of chlorpromazine in plasma by high-performance liquid chromatography with electrochemical detection

A specific and sensitive high-performance liquid chromatographic (HPLC) method for the quantitative determination of subnanogram levels of chlorpromazine in plasma is described. Following extraction of chlorpromazine and the internal standard, prochlorperazine, HPLC analysis is carried out on a cyano column with a mobile phase consisting of 0.1 M ammonium acetate in acetonitrile (10:90 v/v). The use of oxidative thin-layer amperometric detection allowed the quantitation of 0.25 ng of chlorpromazine/ml of plasma with a coefficient of variation of 5.1%. The HPLC method has adequate sensitivity to follow plasma concentration-time profiles up to 24 hr following low single oral doses of chlorpromazine in healthy volunteers.

The presence of 7-hydroxychlorpromazine in CSF of chloropromazine-treated patients

7-Hydroxychlorpromazine (7-OHCPZ) has been identified and quantified in CSF from chlorpromazine (CPZ)-treated schizophrenic patients. The level of the metabolite in CSF was similar to that of CPZ. In serum the amount of 7-OHCPZ was about 30% of CPZ. The concentration of 7-OHCPZ in csf was positively and significantly correlated to the serum level.

Psychotic exacerbation with haloperidol

A case illustrating the worsening of a patient's schizophrenic symptoms following haloperidol dosage increases in presented. This case is remarkable in that few cases of psychotic exacerbation with haloperidol dosage increases have been reported in the world literature. The possibility exists that, like certain tricyclic antidepressants, neuroleptic medication may possess a "therapeutic window,". The concept of a therapeutic window and its relationship to the phenomenon of psychotic exacerbation is reviewed. In evaluating this condition, the clinician should consider other causes of psychotic exacerbation, such as akathisia and anticholinergic psychosis.

The in vivo distribution of an antidepressant drug (DMI) in male and female rats

The accumulation of IP injected 3H-desipramine (DMI) in the brain and in the liver has been studied in both male and female rats. The total amount of DMI in the brains of females is 2 to 4 times that found in the brains of males. In females the amount of DMI is highest on the day of estrus and lowest on proestrus. This sex difference was not found following the injections of another psychoactive drug, 3H-chlorpromazine. In both males and females the level of DMI in the cortex and caudate is slightyl higher than in the hippocampus, septum and hypothalamus. The pharmaco-kinetics and dose dependence of the accumulation of DMI are also similar in males and females. Maximal levels are reached in the liver in less than 15 min, whereas in the brain it takes 30 min. The decline of radioactivity in the liver is faster than in brain. There is no saturation in the amount of DMI taken in brain. There is no saturation in the amount of DMI taken up in brain or liver in the dose range up to 40 mg/kg. The sex difference in the amount of 3H-DMI in brain, which may be the result of sex-dependent metabolism in liver microsomes, may explain the male-female differences in reaction to antidepressants.

The effect of propranolol treatment in shizophrenia on CSF amine metabolites and prolactin

Recent reports have suggested that high doses of propranolol may be an effective treatment in schizophrenia. To determine whether such treatment has effects on cerebrospinal fluid (CSF) amine metabolites and prolactin similar to the effects of the neuroleptic drugs, we studied CSF from ten patients before and after propanolol therapy. The initial CSF sample was removed after a drug-free period and propranolol dosage was then increased over 1 week to 1000 mg daily in all ten patients. A second CSF sample was removed after 3 weeks of propranolol therapy. Propranolol levels and prolactin in CSF were measured by radioimmunoassay. Homovanillic acid, 5-hydroxyindoleacetic acid, and 3-methoxy-4-hydroxyphenylethylene glycol were measured by gas chromatography-mass spectrometry. Propranolol had no effect on the prolactin or amine metabolite concentrations. CSF propranolol levels averaged 40 ng/ml (range less than 1--78).

Clinical effects and drug concentrations in plasma and cerebrospinal fluid in psychotic patients treated with fixed doses of chlorpromazine

The clinical effects of chlorpromazine (CPZ) administered in accordance with a double-blind design in one of three doses (200, 400 or 600 mg) were examined in 44 psychotic patients. The relationships between the effects and the CPZ concentrations in plasma and cerebrospinal fluid (CSF) were analyzed. The antipsychotic and side effects were rated according to the CPRS and the Simpson and Angus scale. CPZ concentrations were measured by a mass fragmentographic method. Treatment with CPZ resulted in a significant reduction of morbidity scores, without any clear dose relation. The final outcome was more favourable in women than in men. Extrapyramidal side effects but not somnolence were positively dose related. The antipsychotic effects tended to be positively related to the dose of CPZ in mg/kg as well as the CPZ concentrations in plasma and CSF. The greatest number of significant correlations between the CPZ concentration in CSF and the morbidity scores were seen after 2 weeks of treatment. The results indicated marked clinical improvement with CPZ concentrations above 1 ng/ml in CSF and 40 ng/ml in plasma. After 4 weeks of treatment the correlations between the CPZ concentrations and the clinical improvement were still positive but the coefficients were lower than at 2 weeks and only occasionaly significant. Extrapyramidal symptoms were significantly related to the CPZ concentrations in plasma and CSF. Somnolence was significantly related to the CPZ concentrations in CSF.

Monoamine metabolite levels in cerebrospinal fluid of psychotic women treated with melperone or thiothixene

Psychotic women with schizophrenic symptoms were treated with melperone 100 mg X 3 (n = 29) or thiothixene 10 mg X 3 (N = 34) USING A DOUBLE-BLIND PROCEDURE. Before and during treatment, levels of HVA, MOPEG, and 5-HIAA, the major metabolites of DA, NE, and 5-HT, were determined in lumbar cerebrospinal fluid by a mass fragmentographic technique. Both treatments resulted in an elevation of the HVA levels after 2 weeks, thiothixene having a more marked effect. The effect of thiothixene but not of melperone persisted after 4 weeks. Thiothixene did not influence the MOPEG level, but melperone reduced it after 4 weeks of treatment. The 5-HIAA levels were not significantly altered by the drugs. The HVA/MOPEG and the HVA/5-HIAA ratios were highly significantly elevated by both drugs after 2 as well as 4 weeks. Thiothixene induced a significantly greater change of these ratios than melperone. The results supply evidence that thiothixene accelerates central dopamine metabolism in man, presumably by blocking DA receptors. Melperone appears to act similarly, but has an effect which is weaker and/or of shorter duration. During long-term treatment with melperone the receptors develop tolerance to it. The acceleration in DA metabolism declines and the effect of melperone switches instead to central NA metabolism. The results indicate that both drugs cause long-term changes in the activity ratios of central monoamine systems. It is suggested that such changes in several systems rather than single biochemical events may be related to the antipsychotic effects of neuroleptic drugs. This study also demonstrated the versatility of using monoamine metabolite analysis of the CSF as a tool for the quantification of biochemical effects of neuroleptic drugs on the human CNS.