clozapine and fluperlapine

The use of fluperlapine and the structurally related clozapine has been associated with the induction of agranulocytosis in humans. Unlike clozapine, fluperlapine is relatively resistant to chemical and biochemical oxidations. In this study we demonstrated that 7-hydroxyfluperlapine, the major metabolite of fluperlapine in humans, is oxidized to a reactive intermediate by HOCl and by myeloperoxidase in the presence of H(2)O(2) and Cl(-). This reactive intermediate was identified as an iminoquinone species with a M + 1 ion at m/z 324 by mass spectrometry. The iminoquinone intermediate was trapped by N-acetyl-L-cysteine (NAC) as well as GSH. NMR spectra of the NAC adducts indicated that the NAC was bound to the 6 and 9 positions of the aromatic ring. This is the same orientation as the binding of nucleophiles to the reactive metabolite of clozapine. We were able to use an antibody against clozapine to demonstrate that 7-hydroxyfluperlapine, but not fluperlapine itself, covalently modifies human myeloperoxidase. Furthermore, we demonstrated that 7-hydroxyfluperlapine is metabolized by activated neutrophils to a reactive intermediate that covalently binds to neutrophils. In the presence of NAC or GSH, such covalent binding was inhibited and the NAC or GSH adducts were formed. Thus, the reactivity and even the orientation of the binding of the reactive metabolite of 7-hydroxyfluperlapine is very similar to that of clozapine. These results provide a mechanism for the formation of a reactive metabolite of fluperlapine similar to clozapine that may explain its ability to induce agranulocytosis.

Topics: Acetylcysteine; Agranulocytosis; Binding, Competitive; Clozapine; Dibenzazepines; Glutathione; Hemocyanins; Humans; Hypochlorous Acid; Immune Sera; Immunoblotting; Neutrophil Activation; Neutrophils; Oxidation-Reduction; Peroxidase; Protein Binding

Clozapine is associated with a high incidence of agranulocytosis. We had previously found that it is oxidized by granulocytes, or simply HOCl, to a reactive metabolite that irreversibly binds to the cells, and we proposed that this reactive metabolite is responsible for clozapine-induced agranulocytosis. The reactive metabolite appeared to be a nitrenium ion formed by chlorination of the nitrogen bridge between the two aromatic rings. If this is correct, analogs that contain this structural feature should also be oxidized to a reactive intermediate while those not possessing this feature would, at least, not form the same type of reactive intermediate and, therefore, may not induce agranulocytosis. We tested the first part of this hypothesis with three clozapine analogs that do contain a nitrogen bridge and three that do not. Consistent with the hypothesis, the three analogs that do contain the nitrogen bridge formed reactive intermediates that could be trapped with glutathione when oxidized by HOCl, myeloperoxidase or activated neutrophils. In contrast, we found no evidence of a reactive intermediate on oxidation of analogs that contained an oxygen or sulfur bridge rather than a nitrogen bridge. If such reactive metabolites are responsible for drug-induced agranulocytosis, it should be possible to use such a simple screening method to test drugs at an early stage in their development for the potential to induce agranulocytosis.

Topics: Agranulocytosis; Antipsychotic Agents; Benzodiazepines; Binding Sites; Chromatography, High Pressure Liquid; Chromatography, Liquid; Clozapine; Dibenzazepines; Glutathione; Granulocytes; Humans; Hydrogen Peroxide; Hypochlorous Acid; Lymphocyte Activation; Mass Spectrometry; Neutrophils; Nitrogen; Olanzapine; Oxidation-Reduction; Peroxidase; Pirenzepine; Structure-Activity Relationship

Antagonists of the N-methyl-D-Aspartate (NMDA) subtype of glutamate receptor (e.g., phencyclidine, ketamine, MK-801) cause a schizophrenia-like psychosis in humans and neurotoxicity in the adult rat brain. We report here that clozapine and structurally related agents (olanzapine, fluperlapine, loxapine, amoxapine) can prevent NMDA antagonist neurotoxicity in the rat with a rank order corresponding to their ability to mimic the antipsychotic properties of clozapine.

Topics: Animals; Antipsychotic Agents; Benzodiazepines; Clozapine; Dibenzazepines; Dibenzoxazepines; Dizocilpine Maleate; Female; N-Methylaspartate; Nervous System; Olanzapine; Pirenzepine; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

A large interindividual variability for clozapine bioavailability and plasma steady-state concentrations and clearance exists. The enzymatic system which is involved in clozapine metabolism has not been fully characterized, yet structurally related tricyclic drugs have been found to be metabolized by cytochrome P450 2D6 (CYP2D6), which is polymorphically expressed in humans. The involvement of CYP2D6 in clozapine and fluperlapine metabolism was studied with human liver microsomes and in recombinant RT2D6 7-8 (RT2D6) cells, which specifically express human CYP2D6. Clozapine and its structural analog fluperlapine both bind to the active site of CYP2D6, as demonstrated by the competitive inhibition of dextromethorphan metabolism at inhibitor concentrations up to 40 microM. The inhibition constants (Ki) for both clozapine and fluperlapine were about 4 microM in microsomes from human liver. Clozapine exhibited a higher inhibition constant of 18.7 microM in microsomes from RT2D6 cells, but the difference was not statistically significant (P less than .05). These concentrations are close to the plasma concentrations of 0.3 to 3 microM achieved during clozapine therapy. Both clozapine and fluperlapine are also metabolized by CYP2D6. RT2D6 cells produced a number of metabolites from clozapine, whereas only a single metabolite was obtained from fluperlapine. The clozapine metabolites were not identified; however, they were different from N-oxide and N-demethyl clozapine. The fluperlapine metabolite was found to be the 7-hydroxy fluperlapine, which is also a major metabolite in vivo. In conclusion, both drug-drug interactions on the binding site of CYP2D6 and polymorphic metabolism of clozapine by CYP2D6 could contribute to the observed variability in clozapine kinetics in humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Base Sequence; Clozapine; Cytochrome P-450 Enzyme System; Dealkylation; Dextromethorphan; Dibenzazepines; Humans; In Vitro Techniques; Microsomes, Liver; Molecular Sequence Data; Recombinant Proteins

The effect of acute treatment with seven atypical antipsychotic drugs and four typical antipsychotic drugs on serotonin2 (5-HT2) receptor binding sites in rat cerebral cortex was studied. Among the atypical antipsychotic drugs examined, clozapine, fluperlapine, RMI-81582 and setoperone decreased the density of 5-HT2 receptors, but ticspirone, amperozide and melperone did not. None of the drugs affected the Kd value. Among the typical antipsychotic drugs, loxapine decreased Bmax and increased the Kd of 5-HT2 receptor binding sites, whereas chlorpromazine and cis-flupenthixol had no effect. Clothiapine, a typical antipsychotic drug of the same chemical class as clozapine, decreased Bmax without increasing Kd. The downregulation of 5-HT2 receptor binding sites following a single injection of clozapine, 20 mg/kg, remained almost unchanged during the first 72 hrs and was still significantly decreased for up to 120 hrs. There was no relationship between the affinity for the downregulation of rat cortical 5-HT2 receptor binding site and 5-HT2 receptor density. Coadministration of the D1 dopamine agonist, SKF-38393, did not affect the clozapine-induced downregulation. It is suggested that rapid and prolonged downregulation of 5-HT2 receptor sites is characteristic of some but not all atypical antipsychotic drugs and is not specific to atypical antipsychotic drugs. Dibenzo-epines (clozapine, loxapine, amoxapine, chlothiapine) consistently downregulate 5-HT2 receptors in frontal cortex after acute treatment.

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; Animals; Antipsychotic Agents; Butyrophenones; Cerebral Cortex; Chlorpromazine; Clozapine; Dibenzazepines; Dibenzothiazepines; Down-Regulation; Flupenthixol; Kinetics; Loxapine; Male; Pyrimidinones; Rats; Rats, Inbred Strains; Receptors, Serotonin; Spiro Compounds; Time Factors

The effects of the two atypical neuroleptics clozapine and fluperlapine on the dopaminergic function in the striatum and in the prefrontal cortex were studied using the transversal microdialysis technique in awake, freely moving rats. Although neither drug induced catalepsy in rats, both increased the release of dopamine (DA) and the output of its metabolites in a similar way in both areas. Unlike classical neuroleptics, after clozapine and fluperlapine administration, the stimulation of DA release was strictly coupled to that of the metabolites, and a second injection was able to renew it. Pretreatment with the selective D1 agonists SKF 38393 or CY 208-243, by themselves ineffective on the release of DA, antagonized the effects of low doses and substantially reduced those of higher doses of clozapine and fluperlapine, indicating that these two atypical drugs act, depending on the dose, selectively or partially through D1 receptors.

Topics: Animals; Antipsychotic Agents; Cerebral Cortex; Clozapine; Corpus Striatum; Dibenzazepines; Dopamine; Male; Rats; Rats, Inbred Strains

Two atypical neuroleptic agents, clozapine and fluperlapine, produced rapid elevations in plasma PRL concentrations that were similar in magnitude to those produced by haloperidol. However, the PRL response to clozapine or fluperlapine was of much shorter duration than that elicited by haloperidol. Clozapine, but neither fluperlapine nor haloperidol, produced a rapid increase in the activity of tuberoinfundibular dopamine (TIDA) neurons, as evidenced by an enhanced accumulation of dihydroxyphenylalanine (DOPA) in the median eminence after the inhibition of DOPA decarboxylase. The clozapine-induced increase in DOPA accumulation was evident within 30 minutes after its administration and persisted for at least 4 hours. The clozapine-induced increase in the activity of TIDA neurons may account, in part, for the abbreviated PRL response to this neuroleptic. In addition, ability to produce a short-lived increase in PRL secretion in the rat appears to be common to the atypical neuroleptic drugs.

Topics: Animals; Clozapine; Dibenzazepines; Dihydroxyphenylalanine; Dopamine; Dose-Response Relationship, Drug; Haloperidol; Hypothalamus; Median Eminence; Neurons; Prolactin; Rats; Rats, Inbred Strains; Time Factors

Fluperlapine has been reported to possess antischizophrenic and antidepressant properties, with low incidence of extrapyramidal side-effects. In order to get more information about the interactions of fluperlapine with rat brain dopaminergic systems, its binding to striatal D2 receptors, measured ex vivo, and its effects on DA metabolism in different brain areas were investigated. Clozapine and haloperidol served as reference compounds in these investigations. It was found that all three agents blocked D2 receptors and increased DA metabolism. Clozapine and fluperlapine differed from haloperidol in that their potency was much lower. Although occupation of striatal D2 receptors by the two dibenzo-epines developed rapidly, the duration was considerably shorter than that of haloperidol. There was no indication that the two dibenzo-epines had a stronger or longer-lasting effect on limbic or cortical DA metabolism compared to that on the striatum. Both drugs caused a weak increase in striatal DA, whereas haloperidol decreased it. It was concluded that the low incidence of extrapyramidal side-effects of fluperlapine, and also of clozapine, is probably due to their weak and relatively brief action on brain DA systems and not due to a selective action on A10 neurotransmission. The anticholinergic properties of the dibenzo-epines might even further reduce the consequences of their already weak effects on DA systems.

Topics: Animals; Brain; Brain Chemistry; Clozapine; Corpus Striatum; Dibenzazepines; Dopamine; Haloperidol; Homovanillic Acid; Male; Rats; Rats, Inbred Strains; Receptors, Dopamine; Receptors, Dopamine D2

It has been shown previously that typical neuroleptics have higher affinities for 3,4-dihydroxyphenylethylamine (dopamine) D1 receptors as labeled by (R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1-N-3-benzazepine- 7-ol ([3H]SCH 23390) than for inhibiting dopamine-stimulated adenylate cyclase. We now report that the atypical neuroleptics, clozapine and fluperlapine, exhibit characteristics opposite to typical neuroleptics, i.e., they have higher affinity for inhibiting dopamine-stimulated adenylate cyclase than [3H]SCH 23390 binding. A variety of compounds, i.e., clozapine, fluperlapine, and dopamine, were tested for their capacity to affect the rate constants of [3H]SCH 23390 binding. Treatment of striatal membranes with phospholipase A2 (PLA2) caused a rapid decrease in the Bmax value of the [3H]SCH 23390 binding with no effect on the KD value. The adenylate cyclase, both the unstimulated, the dopamine-, fluoride-, and forskolin-stimulated activity, was far less sensitive than [3H]SCH 23390 binding to PLA2. Treatment of striatal membranes with filipine and (NH4)2SO4 produced, as did PLA2 treatment, a rapid decline in [3H]SCH 23390 binding. However, opposite to PLA2 treatment, these agents stimulated the adenylate cyclase. In conclusion, a comparison of the pharmacological characteristics of [3H]SCH 23390 binding and dopamine-stimulated adenylate cyclase suggests the existence of two different D1 binding sites. The rate experiments exclude the possibility of allosterically coupled sites. Instead our results favor that the D1 receptor exists in different states/conformations, i.e., both adenylate cyclase-coupled and uncoupled, and further, that the atypical neuroleptics clozapine and fluperlapine may have adenylate cyclase-coupled dopamine D1 receptors as target.

Topics: Adenylyl Cyclases; Animals; Benzazepines; Binding Sites; Clozapine; Colforsin; Corpus Striatum; Dibenzazepines; Dopamine; Humans; Kinetics; Phospholipases A; Phospholipases A2; Rats; Receptors, Dopamine; Receptors, Dopamine D1; Synaptic Membranes

A total of 13 patients with drug-induced psychosis in Parkinson's disease were treated with two non-classical neuroleptics-clozapine and fluperlapine. Patients mainly complained about severe hallucinatory symptoms and different degrees of paranoid delusions. Complete relief was observed in 8 patients, moderate improvement in 3 and no effects in 2. Parkinsonian disability did not increase under neuroleptic medication with clozapine and fluperlapine, but could be ameliorated by additional L-dopa or bromocriptine medication. The non-classical neuroleptics employed are dopamine D2 blocking agents with a preferential binding to mesolimbic, mesocortical and hippocampal D2 receptors and no substantial binding to striatal dopamine receptors. Restricted use of these two neuroleptics is necessitated because of the danger of agranulocytosis.

Topics: Aged; Antipsychotic Agents; Benserazide; Bromocriptine; Clozapine; Delusions; Dibenzazepines; Dose-Response Relationship, Drug; Drug Therapy, Combination; Hallucinations; Humans; Hydrazines; Levodopa; Male; Middle Aged; Parkinson Disease; Psychoses, Substance-Induced; Tryptophan

3-Fluoro-6-(4-methyl-piperazinyl)- 11H -dibenz [b,e]azepine ( fluperlapine , NB 106-689) resembles clozapine qualitatively and quantitatively in that it causes sedation, muscle relaxation, anticholinergic effects, no catalepsy, has little effect on apomorphine- and amphetamine-induced behaviour, does not induce apomorphine supersensitivity, and increases dozing and spindle activity in the rat's EEG. In the striatum of rats, it binds less to dopamine (DA) D2-receptor sites, but it enhances DA-turnover more than clozapine. Like clozapine and unlike haloperidol, it is equally active in the striatum, the nucl . accumbens and the cortex. Unlike clozapine, it does not significantly enhance norepinephrine (noradrenaline, NA)- or 5-hydroxytryptamine turnover and it does not increase prolactin blood levels significantly. Of the two compounds, only fluperlapine has some effects in common with antidepressants, i.e. tetrabenazine-antagonism and NA-uptake inhibition in slices of rat brain in vitro and ex vivo.

Topics: Animals; Antidepressive Agents; Antipsychotic Agents; Apomorphine; Binding, Competitive; Brain Chemistry; Clozapine; Dibenzazepines; Dopamine; Electroencephalography; Homovanillic Acid; Humans; Prolactin; Rats; Rats, Inbred Strains; Receptors, Dopamine; Spiperone; Stereotyped Behavior