Clozapine-N-oxide protects dopaminergic neurons against rotenone-induced neurotoxicity by preventing ferritinophagy-mediated ferroptosis

Parkinson's disease (PD) is the second most common neurodegenerative disorder, yet treatment options are limited. Clozapine (CLZ), an antipsychotic used for schizophrenia, has potential as a PD treatment. CLZ and its metabolite, Clozapine-N-Oxide (CNO), show neuroprotective effects on dopaminergic neurons, with mechanisms needing further investigation. This study aimed to confirm the neuroprotective effects of CLZ and CNO in a rotenone-induced mouse model and further explore the underlying mechanisms of CNO-afforded protection. Gait pattern and rotarod activity evaluations showed motor impairments in rotenone-exposed mice, with CLZ or CNO administration ameliorating behavioral deficits. Cell counts and biochemical analysis demonstrated CLZ and CNO's effectiveness in reducing rotenone-induced neurodegeneration of dopaminergic neurons in the nigrostriatal system in mice. Mechanistic investigations revealed that CNO suppressed rotenone-induced ferroptosis of dopaminergic neurons by rectifying iron imbalances, curtailing lipid peroxidation, and mitigating mitochondrial morphological changes. CNO also reversed autolysosome and ferritinophagic activation in rotenone-exposed mice. SH-SY5Y cell cultures validated these findings, indicating ferritinophage involvement, where CNO-afforded protection was diminished by ferritinophagy enhancers. Furthermore, knockdown of NCOA4, a crucial cargo receptor for ferritin degradation in ferritinophagy, hampered rotenone-induced ferroptosis and NCOA4 overexpression countered the anti-ferroptotic effects of CNO. Whereas, iron-chelating agents and ferroptosis enhancers had no effect on the anti-ferritinophagic effects of CNO in rotenone-treated cells. In summary, CNO shielded dopaminergic neurons in the rotenone-induced PD model by modulating NCOA4-mediated ferritinophagy, highlighting a potential therapeutic pathway for PD treatment. This research provided insights into the role of NCOA4 in ferroptosis and suggested new approaches for PD therapy.

Involvement of Extracellular Vesicles in the Proinflammatory Response to Clozapine: Implications for Clozapine-Induced Agranulocytosis

Most idiosyncratic drug reactions (IDRs) appear to be immune-mediated, but mechanistic events preceding severe reaction onset remain poorly defined. Damage-associated molecular patterns (DAMPs) may contribute to both innate and adaptive immune phases of IDRs, and changes in extracellular vesicle (EV) cargo have been detected post-exposure to several IDR-associated drugs. To explore the hypothesis that EVs are also a source of DAMPs in the induction of the immune response preceding drug-induced agranulocytosis, the proteome and immunogenicity of clozapine- (agranulocytosis-associated drug) and olanzapine- (non-agranulocytosis-associated drug) exposed EVs were compared in two preclinical models: THP-1 macrophages and Sprague-Dawley rats. Compared with olanzapine, clozapine induced a greater increase in the concentration of EVs enriched from both cell culture media and rat serum. Moreover, treatment of drug-naïve THP-1 cells with clozapine-exposed EVs induced an inflammasome-dependent response, supporting a potential role for EVs in immune activation. Proteomic and bioinformatic analyses demonstrated an increased number of differentially expressed proteins with clozapine that were enriched in pathways related to inflammation, myeloid cell chemotaxis, wounding, transforming growth factor-β signaling, and negative regulation of stimuli response. These data indicate that, although clozapine and olanzapine exposure both alter the protein cargo of EVs, clozapine-exposed EVs carry mediators that exhibit significantly greater immunogenicity. Ultimately, this supports the working hypothesis that drugs associated with a risk of IDRs induce cell stress, release of proinflammatory mediators, and early immune activation that precedes severe reaction onset. Further studies characterizing EVs may elucidate biomarkers that predict IDR risk during development of drug candidates. SIGNIFICANCE STATEMENT: This work demonstrates that clozapine, an idiosyncratic drug-induced agranulocytosis (IDIAG)-associated drug, but not olanzapine, a safer structural analogue, induces an acute proinflammatory response and increases extracellular vesicle (EV) release in two preclinical models. Moreover, clozapine-exposed EVs are more immunogenic, as measured by their ability to activate inflammasomes, and contain more differentially expressed proteins, highlighting a novel role for EVs during the early immune response to clozapine and enhancing our mechanistic understanding of IDIAG and other idiosyncratic reactions.

The cardiovascular toxicity of clozapine in embryonic zebrafish and RNA sequencing-based transcriptome analysis

Clozapine (CLZ) is the most prescribed medication for treating refractory schizophrenia but is associated with significant cardiovascular toxicity. This study aimed to investigate the cardiovascular toxicity induced by CLZ using zebrafish as a model animal. For this purpose, zebrafish developed to 80-h post-fertilization were exposed to different CLZ concentration solutions for 24 h followed by cardiac morphological observations in yolk sac edema, pericardial edema, and blood coagulation, in addition to increased SV-BA distance, functionally manifested as bradycardia, and decreased cardiac ejection fraction using the untreated embryos as control. At the same time, RNA sequencing was used to study the possible molecular mechanism of CLZ-induced cardiovascular toxicity. The results indicated that compared to the control group, the experimental groups possessed a total of 5888 differentially expressed genes (DEGs), where gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment of analysis indicated that DEGs were mainly enriched in the pathways related to ion channels. These findings may provide new insights and directions for the subsequent in-depth study of the molecular mechanism of CLZ-induced cardiovascular toxicity.

Clozapine suppresses NADPH oxidase activation, counteracts cytosolic H2O2, and triggers early onset mitochondrial dysfunction during adipogenesis of human liposarcoma SW872 cells

Long-term treatment of schizophrenia with clozapine (CLZ), an atypical antipsychotic drug, is associated with an increased incidence of metabolic disorders mediated by poorly understood mechanisms. We herein report that CLZ, while slowing down the morphological changes and lipid accumulation occurring during SW872 cell adipogenesis, also causes an early (day 3) inhibition of the expression/nuclear translocation of CAAT/enhancer-binding protein β and peroxisome proliferator-activated receptor γ. Under the same conditions, CLZ blunts NADPH oxidase-derived reactive oxygen species (ROS) by a dual mechanism involving enzyme inhibition and ROS scavenging. These effects were accompanied by hampered activation of the nuclear factor (erythroid-derived2)-like 2 (Nrf2)-dependent antioxidant responses compared to controls, and by an aggravated formation of mitochondrial superoxide. CLZ failed to exert ROS scavenging activities in the mitochondrial compartment but appeared to actively scavenge cytosolic H2O2 derived from mitochondrial superoxide. The early formation of mitochondrial ROS promoted by CLZ was also associated with signs of mitochondrial dysfunction. Some of the above findings were recapitulated using mouse embryonic fibroblasts. We conclude that the NADPH oxidase inhibitory and cytosolic ROS scavenging activities of CLZ slow down SW872 cell adipogenesis and suppress their Nrf2 activation, an event apparently connected with increased mitochondrial ROS formation, which is associated with insulin resistance and metabolic syndrome. Thus, the cellular events characterised herein may help to shed light on the more detailed molecular mechanisms explaining some of the adverse metabolic effects of CLZ.

Molecular dynamics and free energy calculations of clozapine bound to D2 and H1 receptors reveal a cardiometabolic mitigated derivative

Most atypical antipsychotics derive from a high dropout of drug treatments due to adverse cardiometabolic side effects. These side effects are caused, in part, by the H1 receptor blockade. The current work sought a clozapine derivative with a reduced affinity for the H1 receptor while maintaining its therapeutic effect linked to D2 receptor binding. Explicit molecular dynamics simulations and end-point free energy calculations of clozapine in complex with the D2 and H1 receptors embedded in cholesterol-rich lipid bilayers were performed to analyze the intermolecular interactions and address the relevance of clozapine-functional groups. Based on that, free energy perturbation calculations were performed to measure the change in free energy of clozapine structural modifications. Our results indicate the best clozapine derivative is the iodine atom substitution for chlorine. The latter is mainly due to electrostatic interaction loss for the H1 receptor, while the halogen orientation out of the D2 active site reduces the impact on the affinity.Communicated by Ramaswamy H. Sarma.

Exploring the mechanisms of clozapine-induced blood-brain barrier dysfunction using untargeted metabolomics and cellular metabolism analysis

Brain microvascular endothelial cells (BMVECs) from the blood- brain barrier form a highly selective membrane that protects the brain from circulating blood and maintains a stable microenvironment for the central nervous system. BMVEC dysfunction has been implicated in a variety of neurological and psychiatric disorders. Clozapine, a widely used antipsychotics, has been demonstrated to alter the permeability of BMVECs, but the underlying mechanisms of this effect are not fully understood. In this study, we investigated the effects of clozapine in BMVECs using untargeted metabolomics analysis. Our results illustrated that treatment with clozapine led to significant changes in the metabolic profile of BMVECs, including alterations in amino acid and energy metabolism. These findings suggest that clozapine affects BMVEC permeability through its effects on cellular metabolism. Our study could inform the development of more targeted and effective treatments for understanding the relationships among clozapine, cellular metabolism, and BMVECs in more detail.

Self-Assembling Lecithin-Based Mixed Polymeric Micelles for Nose to Brain Delivery of Clozapine: In-vivo Assessment of Drug Efficacy via Radiobiological Evaluation

Purpose

The research objective is to design intranasal brain targeted CLZ loaded lecithin based polymeric micelles (CLZ- LbPM) aiming to improve central systemic CLZ bioavailability.

Methods

In our study, intranasal CLZ loaded lecithin based polymeric micelles (CLZ- LbPM) were formulated using soya phosphatidyl choline (SPC) and sodium deoxycholate (SDC) with different CLZ:SPC:SDC ratios via thin film hydration technique aiming to enhance drug solubility, bioavailability and nose to brain targeting efficiency. Optimization of the prepared CLZ-LbPM using Design-Expert® software was achieved showing that M6 which composed of (CLZ:SPC: SDC) in respective ratios of 1:3:10 was selected as the optimized formula. The optimized formula was subjected to further evaluation tests as, Differential Scanning Calorimetry (DSC), TEM, in vitro release profile, ex vivo intranasal permeation and in vivo biodistribution.

Results

The optimized formula with the highest desirability exhibiting (0.845), small particle size (12.23±4.76 nm), Zeta potential of (-38 mV), percent entrapment efficiency of > 90% and percent drug loading of 6.47%. Ex vivo permeation test showed flux value of 27 μg/cm².h and the enhancement ratio was about 3 when compared to the drug suspension, without any histological alteration. The radioiodinated clozapine ([¹³¹I] iodo-CLZ) and radioiodinated optimized formula ([¹³¹I] iodo-CLZ-LbPM) were formulated in an excellent radioiodination yield more than 95%. In vivo biodistribution studies of [¹³¹I] iodo-CLZ-LbPM showed higher brain uptake (7.8%± 0.1%ID/g) for intranasal administration with rapid onset of action (at 0.25 h) than the intravenous formula. Its pharmacokinetic behavior showed relative bioavailability, direct transport percentage from nose to brain and drug targeting efficiency of 170.59%, 83.42% and 117% respectively.

Conclusion

The intranasal self-assembling lecithin based mixed polymeric micelles could be an encouraging way for CLZ brain targeting.

Evidence that GIRK Channels Mediate the DREADD-hM4Di Receptor Activation-Induced Reduction in Membrane Excitability of Striatal Medium Spiny Neurons

The hM4Di receptor-based chemogenetic DREADD system has been widely used to suppress neuronal activities, which has contributed substantially to the identification of behavior-associated neuronal circuitries including those in the striatum. One major mechanism by which hM4Di receptor activation suppresses neuronal activity is that the activation reduces membrane excitability, which is thought to be mediated by the opening of GIRK channels. However, previous studies have suggested that GIRK channels are barely expressed in the striatum, which naturally raises the question whether the hM4Di receptor activation-induced reduction in membrane excitability found in striatal medium spiny neurons (MSNs, which constitute 95-98% of the striatal neuronal population) is truly mediated by the endogenous GIRK channels in such scarcity. This study aims to answer this question by applying a GIRK channel-selective blocker, tertiapin-Q (TPNQ), to striatal MSNs. This study first verified that application of clozapine (CZP), an hM4Di receptor agonist, to MSNs expressing the hM4Di receptors hyperpolarized the cell membrane, and reduced membrane excitability and input resistance. This study next revealed that TPNQ post-treatment completely canceled the above CZP-induced electrophysiological effects and that TPNQ pretreatment mostly prevented further expression of the above CZP-induced electrophysiological effects. In addition, confocal microscopy imaging also revealed significant above-background GIRK1 immunofluorescence signals in striatal MSNs. These data suggest that the TPNQ-sensitive GIRK channels, despite being expressed at low levels, are likely the major mediator downstream of hM4Di receptor activation to reduce membrane excitability in striatal MSNs. These results imply that the notion held by scientists in the field that GIRK channels are absent in the striatum or their expression level is not significant enough to exert any function might be oversimplified or incorrect.

[A novel ligand for chemogenetic receptors, Deschloroclozapine, enables rapid and selective modulation of neuronal activity and behavior in living animals]

A brain function is manifested by harmonizing some brain regions responsible for the function. Since pathological conditions in neuropsychiatric disorders are induced by the failure of this mechanism, it is crucial to identify the affected function by manipulating the specific brain regions. Designer receptors exclusively activated by designer drugs (DREADDs) are one of the chemogenetic tools that offer a means to repeatedly reversible control of the activity of a target neural population expressing a "designer receptor" by systemic injection of "designer drug," which is biologically inert. The most widely used DREADDs are muscarinic-based receptors, such as hM3Dq (excitatory) and hM4Di (inhibitory), which can be activated by clozapine-N-oxide (CNO). However, CNO has some concerns. First, because CNO has a modest brain penetrability, the effect is slow. Second, since CNO is metabolized to clozapine, an antipsychotic drug that acts on numerous endogenous receptors, the systemic administration may produce off-target actions. Therefore, we developed a new compound, deschloroclozapine (DCZ), to solve these issues. DCZ has a higher affinity and greater agonist potency than CNO with reduced off-target actions and can rapidly modulate the neuronal activity and behavior with muscarinic-based DREADDs in living animals. Given the potential weak point of CNO, DCZ affords clear benefits to many users of muscarinic-based DREADD, with increased reliability by removing concerns about possible off-target responses.

Evidence in primates supporting the use of chemogenetics for the treatment of human refractory neuropsychiatric disorders

Non-human primate (NHP) models are essential for developing and translating new treatments that target neural circuit dysfunction underlying human psychopathology. As a proof-of-concept for treating neuropsychiatric disorders, we used a NHP model of pathological anxiety to investigate the feasibility of decreasing anxiety by chemogenetically (DREADDs [designer receptors exclusively activated by designer drugs]) reducing amygdala neuronal activity. Intraoperative MRI surgery was used to infect dorsal amygdala neurons with AAV5-hSyn-HA-hM4Di in young rhesus monkeys. In vivo microPET studies with [11C]-deschloroclozapine and postmortem autoradiography with [3H]-clozapine demonstrated selective hM4Di binding in the amygdala, and neuronal expression of hM4Di was confirmed with immunohistochemistry. Additionally, because of its high affinity for DREADDs, and its approved use in humans, we developed an individualized, low-dose clozapine administration strategy to induce DREADD-mediated amygdala inhibition. Compared to controls, clozapine selectively decreased anxiety-related freezing behavior in the human intruder paradigm in hM4Di-expressing monkeys, while coo vocalizations and locomotion were unaffected. These results are an important step in establishing chemogenetic strategies for patients with refractory neuropsychiatric disorders in which amygdala alterations are central to disease pathophysiology.

Bioactivation of clozapine by mitochondria of the murine heart: Possible cause of cardiotoxicity

The mechanism of clozapine-associated cardiotoxicity has not been elucidated. The formation of a reactive nitrenium ion from the drug has been suggested as the cause, however, the reason why the heart is a target remains unknown. The heart is one of the most perfused organs; therefore, it contains a large number of mitochondria per cell; these organelles are responsible for both oxygen metabolism and energy production due to high energy expenditure. Given that mitochondria play critical roles in cellular homeostasis and maintenance, this study tested the hypothesis that cardiac mitochondria are both a target and initiator of clozapine-induced cardiotoxicity through activating the drug. We investigated whether murine heart receives a relatively high amount of systemically administered drug (20 mg/kg, i.p., Wistar albino rats) and whether cardiac mice (Swiss albino) and rat (Wistar albino) mitochondria locally activate clozapine (100 μM) to a reactive metabolite. We observed a relatively large distribution of clozapine to heart tissue as well as the formation of reactive metabolites by cardiac mitochondria in situ. Mitochondrial cytochrome P450 enzymes (CYP) in cardiac tissue responsible for biotransformation of clozapine were also characterized. CYP3A4 has been found to be the major enzyme catalyzes CLZ bioactivation, while CYP1A largely and CYP3A4 partially catalyzes the formation of stable metabolites of CLZ. At 100 μM concentration, clozapine caused a significant decline in mitochondrial oxygen consumption rate in vitro as much as positive control (antimycin A), while it did not induce mitochondrial permeability transition pore opening. These data provide an explanation as to why the heart is a target for clozapine adverse effects.

Pharmacogenomic Variants and Drug Interactions Identified Through the Genetic Analysis of Clozapine Metabolism

OBJECTIVE

Clozapine is the only effective medication for treatment-resistant schizophrenia, but its worldwide use is still limited because of its complex titration protocols. While the discovery of pharmacogenomic variants of clozapine metabolism may improve clinical management, no robust findings have yet been reported. This study is the first to adopt the framework of genome-wide association studies (GWASs) to discover genetic markers of clozapine plasma concentrations in a large sample of patients with treatment-resistant schizophrenia.

METHODS

The authors used mixed-model regression to combine data from multiple assays of clozapine metabolite plasma concentrations from a clozapine monitoring service and carried out a genome-wide analysis of clozapine, norclozapine, and their ratio on 10,353 assays from 2,989 individuals. These analyses were adjusted for demographic factors known to influence clozapine metabolism, although it was not possible to adjust for all potential mediators given the available data. GWAS results were used to pinpoint specific enzymes and metabolic pathways and compounds that might interact with clozapine pharmacokinetics.

RESULTS

The authors identified four distinct genome-wide significant loci that harbor common variants affecting the metabolism of clozapine or its metabolites. Detailed examination pointed to coding and regulatory variants at several CYP* and UGT* genes as well as corroborative evidence for interactions between the metabolism of clozapine, coffee, and tobacco. Individual effects of single single-nucleotide polymorphisms (SNPs) fine-mapped from these loci were large, such as the minor allele of rs2472297, which was associated with a reduction in clozapine concentrations roughly equivalent to a decrease of 50 mg/day in clozapine dosage. On their own, these single SNPs explained from 1.15% to 9.48% of the variance in the plasma concentration data.

CONCLUSIONS

Common genetic variants with large effects on clozapine metabolism exist and can be found via genome-wide approaches. Their identification opens the way for clinical studies assessing the use of pharmacogenomics in the clinical management of patients with treatment-resistant schizophrenia.

Tracking the Time-Dependent Role of the Hippocampus in Memory Recall Using DREADDs

The hippocampus is critical for the storage of new autobiographical experiences as memories. Following an initial encoding stage in the hippocampus, memories undergo a process of systems-level consolidation, which leads to greater stability through time and an increased reliance on neocortical areas for retrieval. The extent to which the retrieval of these consolidated memories still requires the hippocampus is unclear, as both spared and severely degraded remote memory recall have been reported following post-training hippocampal lesions. One difficulty in definitively addressing the role of the hippocampus in remote memory retrieval is the precision with which the entire volume of the hippocampal region can be inactivated. To address this issue, we used Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), a chemical-genetic tool capable of highly specific neuronal manipulation over large volumes of brain tissue. We find that remote (>7 weeks after acquisition), but not recent (1–2 days after acquisition) contextual fear memories can be recalled after injection of the DREADD agonist (CNO) in animals expressing the inhibitory DREADD in the entire hippocampus. Our data demonstrate a time-dependent role of the hippocampus in memory retrieval, supporting the standard model of systems consolidation.

Optimising plasma levels of clozapine during metabolic interactions: a review and case report with adjunct rifampicin treatment

BACKGROUND

Clozapine is the only licensed medication for treatment-resistant schizophrenia. The metabolism of clozapine is affected by multiple pharmacokinetic interactions, so the co-administration of adjunct medications can have a significant clinical effect. The anti- tuberculosis medication rifampicin is a potent inducer of the cytochrome P450 system and therefore can cause a reduction in the plasma concentration of clozapine. There is limited clinical evidence regarding co-administration of these medications; in particular there is a lack of data regarding the effect on plasma clozapine levels, which is the key factor determining clinical efficacy. This is clinically relevant given evidence of an increased risk of tuberculosis in patients with schizophrenia.

CASE PRESENTATION

We present a case of a 28 year old British man with a diagnosis of schizoaffective disorder who presented with persistent psychotic symptoms. He developed a systemic inflammatory condition, diagnosed as tuberculosis, and was commenced on a six month course of treatment that included rifampicin. This case presents comprehensive data to illustrate the effect on clozapine plasma levels of a complete course of tuberculosis therapy.

CONCLUSION

This case report provides guidance to clinicians in managing drug interactions between clozapine and rifampicin to enable safe and effective treatment. The co-administration of these medications is likely to increase as the existing underuse of clozapine is recognised whilst the incidence of tuberculosis increases.

Glutathione trapping of reactive drug metabolites produced by biomimetic metalloporphyrin catalysts

RATIONALE

Metalloporphyrins can be useful in the production of drug metabolites, as they enable easier production of oxidative metabolites usually produced by the cytochrome P450 enzymes. Our aim was to test metalloporphyrin-based biomimetic oxidation (BMO) methods for production and S-glutathione trapping of reactive drug metabolites in addition to phase I metabolites.

METHODS

Clozapine, ticlopidine and citalopram were selected as model compounds. These were incubated with the BMO assay and the incubations were analyzed with high-resolution liquid chromatography/mass spectrometry (LC/MS) and tandem mass spectrometry (LC/MS/MS). Additionally, incubations with human liver S9 fraction were performed to compare the results with the BMO assay.

RESULTS

Six glutathione conjugates were identified for clozapine from the S9 incubation, while the BMO assay produced four of these. Four out of the five phase I metabolites produced by S9 were detected using the BMO assay. For ticlopidine, four glutathione conjugates were detected from the S9 incubation, but none of these were observed using the BMO assay. Eight of the nine phase I metabolites produced by S9 incubation were detected in the BMO assay. As expected, no glutathione conjugates were detected for citalopram, and the same three phase I metabolites were detected in both S9 and BMO incubations.

CONLUSIONS

Differences in formation of GSH-trapped reactive metabolites by BMO assay between clozapine and ticlopidine are probably due to different reactive intermediates and reaction mechanisms. The reactive intermediate of clozapine, the nitrenium ion was generated, but the reactive intermediates of ticlopidine, S-oxide and epoxide, were not detected from the incubations. However, the results show that for selected cases the use of biomimetic assays can be used to produce high amounts of S-glutathione conjugates identical to those from liver subfraction incubations, on a scale that is relevant for purification and subsequent identification by NMR spectroscopy; which is often difficult using incubations with liver subfractions.

A semi-supervised method for drug-target interaction prediction with consistency in networks

Computational prediction of interactions between drugs and their target proteins is of great importance for drug discovery and design. The difficulties of developing computational methods for the prediction of such potential interactions lie in the rarity of known drug-protein interactions and no experimentally verified negative drug-target interaction sample. Furthermore, target proteins need also to be predicted for some new drugs without any known target interaction information. In this paper, a semi-supervised learning method NetCBP is presented to address this problem by using labeled and unlabeled interaction information. Assuming coherent interactions between the drugs ranked by their relevance to a query drug, and the target proteins ranked by their relevance to the hidden target proteins of the query drug, we formulate a learning framework maximizing the rank coherence with respect to the known drug-target interactions. When applied to four classes of important drug-target interaction networks, our method improves previous methods in terms of cross-validation and some strongly predicted interactions are confirmed by the publicly accessible drug target databases, which indicates the usefulness of our method. Finally, a comprehensive prediction of drug–target interactions enables us to suggest many new potential drug–target interactions for further studies.

[A patient on clozapine in the general hospital: the need for discussion between specialists from different disciplines and for close monitoring of the patient's plasma level]

A 49-year-old man being treated with clozapine for schizophrenia was prescribed ciprofloxacin because of bile spill following cholecystectomy. Four days after surgery he showed symptoms of clozapine intoxication, probably because the ciprofloxacin had inhibited CYP1A2. Over the next few days the patient's plasma level was measured frequently but without any real sense of urgency. As a result, the patient's plasma level remained too high for a long period, then decreased, the decrease being accompanied by the recurrence of psychotic symptoms. Our advice, therefore, is that if a patient on clozapine is in a general hospital there needs to be pro-active discussion of the case between a psychiatrist and other medical specialists and the patient's clozapine plasma level should be measured whenever the patient's condition appears to be deteriorating.

Spectroscopic and molecular modeling evidence of clozapine binding to human serum albumin at subdomain IIA

Various spectroscopy and molecular docking methods were used to examine the binding of Clozapine (CLZ) to human serum albumin (HSA) in this paper. By monitoring the intrinsic fluorescence of single Trp214 residue and performing Dansylamide (DNSA) displacement measurement, the specific binding of CLZ in the vicinity of Sudlow's Site I of HSA has been clarified. An apparent distance of 27.3 Å between the Trp214 and CLZ was obtained via fluorescence resonance energy transfer (FRET) method. In addition, the changes in the secondary structure of HSA after its complexation with CLZ ligand were studied with CD spectroscopy, which indicate that CLZ does not has remarkable effect on the structure of the protein. Moreover, thermal denaturation experiment shows that the HSA-CLZ complexes are conformationally more stable. Finally, the binding details between CLZ and HSA were further confirmed by molecular docking studies, which revealed that CLZ was bound at subdomain IIA through multiple interactions, such as hydrophobic effect, van der Waals forces and hydrogen bonding.

Impaired respiratory and body temperature control upon acute serotonergic neuron inhibition

Physiological homeostasis is essential for organism survival. Highly responsive neuronal networks are involved, but their constituent neurons are just beginning to be resolved. To query brain serotonergic neurons in homeostasis, we used a neuronal silencing tool, mouse RC::FPDi (based on the synthetic G protein-coupled receptor Di), designed for cell type-specific, ligand-inducible, and reversible suppression of action potential firing. In mice harboring Di-expressing serotonergic neurons, administration of the ligand clozapine-N-oxide (CNO) by systemic injection attenuated the chemoreflex that normally increases respiration in response to tissue carbon dioxide (CO(2)) elevation and acidosis. At the cellular level, CNO suppressed firing rate increases evoked by CO(2) acidosis. Body thermoregulation at room temperature was also disrupted after CNO triggering of Di; core temperatures plummeted, then recovered. This work establishes that serotonergic neurons regulate life-sustaining respiratory and thermoregulatory networks, and demonstrates a noninvasive tool for mapping neuron function.

Pharmacogenetic modulation of orexin neurons alters sleep/wakefulness states in mice

Hypothalamic neurons expressing neuropeptide orexins are critically involved in the control of sleep and wakefulness. Although the activity of orexin neurons is thought to be influenced by various neuronal input as well as humoral factors, the direct consequences of changes in the activity of these neurons in an intact animal are largely unknown. We therefore examined the effects of orexin neuron-specific pharmacogenetic modulation in vivo by a new method called the Designer Receptors Exclusively Activated by Designer Drugs approach (DREADD). Using this system, we successfully activated and suppressed orexin neurons as measured by Fos staining. EEG and EMG recordings suggested that excitation of orexin neurons significantly increased the amount of time spent in wakefulness and decreased both non-rapid eye movement (NREM) and rapid eye movement (REM) sleep times. Inhibition of orexin neurons decreased wakefulness time and increased NREM sleep time. These findings clearly show that changes in the activity of orexin neurons can alter the behavioral state of animals and also validate this novel approach for manipulating neuronal activity in awake, freely-moving animals.

Improved detection of reactive metabolites with a bromine-containing glutathione analog using mass defect and isotope pattern matching

Drug bioactivation leading to the formation of reactive species capable of covalent binding to proteins represents an important cause of drug-induced toxicity. Reactive metabolite detection using in vitro microsomal incubations is a crucial step in assessing potential toxicity of pharmaceutical compounds. The most common method for screening the formation of these unstable, electrophilic species is by trapping them with glutathione (GSH) followed by liquid chromatography/mass spectrometry (LC/MS) analysis. The present work describes the use of a brominated analog of glutathione, N-(2-bromocarbobenzyloxy)-GSH (GSH-Br), for the in vitro screening of reactive metabolites by LC/MS. This novel trapping agent was tested with four drug compounds known to form reactive metabolites, acetaminophen, fipexide, trimethoprim and clozapine. In vitro rat microsomal incubations were performed with GSH and GSH-Br for each drug with subsequent analysis by liquid chromatography/high-resolution mass spectrometry on an electrospray time-of-flight (ESI-TOF) instrument. A generic LC/MS method was used for data acquisition, followed by drug-specific processing of accurate mass data based on mass defect filtering and isotope pattern matching. GSH and GSH-Br incubations were compared to control samples using differential analysis (Mass Profiler) software to identify adducts formed via the formation of reactive metabolites. In all four cases, GSH-Br yielded improved results, with a decreased false positive rate, increased sensitivity and new adducts being identified in contrast to GSH alone. The combination of using this novel trapping agent with powerful processing routines for filtering accurate mass data and differential analysis represents a very reliable method for the identification of reactive metabolites formed in microsomal incubations.

Rapid screening and characterization of drug metabolites using multiple ion monitoring dependent product ion scan and postacquisition data mining on a hybrid triple quadrupole-linear ion trap mass spectrometer

Multiple ion monitoring (MIM)-dependent acquisition with a triple quadrupole-linear ion trap mass spectrometer (Q-trap) was previously developed for drug metabolite profiling. In the analysis, multiple predicted metabolite ions are monitored in both Q1 and Q3 regardless of their fragmentations. The collision energy in Q2 is set to a low value to minimize fragmentation. Once an expected metabolite is detected by MIM, enhanced product ion (EPI) spectral acquisition of the metabolite is triggered. To analyze in vitro metabolites, MIM-EPI retains the sensitivity and selectivity similar to that of multiple reaction monitoring (MRM)-EPI in the analysis of in vitro metabolites. Here we present an improved approach utilizing MIM-EPI for data acquisition and multiple data mining techniques for detection of metabolite ions and recovery of their MS/MS spectra. The postacquisition data processing tools included extracted ion chromatographic analysis, product ion filtering and neutral loss filtering. The effectiveness of this approach was evaluated by analyzing oxidative metabolites of indinavir and glutathione (GSH) conjugates of clozapine and 4-ethylphenol in liver microsome incubations. Results showed that the MIM-EPI-based data mining approach allowed for comprehensive detection of metabolites based on predicted protonated molecules, product ions or neutral losses without predetermination of the parent drug MS/MS spectra. Additionally, it enabled metabolite detection and MS/MS acquisition in a single injection. This approach is potentially useful in high-throughout screening of metabolic soft spots and reactive metabolites at the drug discovery stage.

An algorithm for thorough background subtraction from high-resolution LC/MS data: application for detection of glutathione-trapped reactive metabolites

A control sample background-subtraction algorithm was developed for thorough subtraction of background and matrix-related signals in high-resolution, accurate mass liquid chromatography/mass spectrometry (LC/MS) data to reveal ions of interest in an analyte sample. This algorithm checked all ions in the control scans within a specified time window around the analyte scan for potential subtraction of ions found in that analyte scan. Applying this method, chromatographic fluctuations between runs were dealt with and background and matrix-related signals in the sample could be thoroughly subtracted. The effectiveness of this algorithm was demonstrated using four test compounds, clozapine, diclofenac, imipramine, and tacrine, to reveal glutathione (GSH)-trapped reactive metabolites after incubation with human liver microsomes supplemented with GSH (30 microM compound, 45-min incubation). Using this algorithm with a+/-1.0 min control scan time window, a+/-5 ppm mass error tolerance, and appropriate control samples, the GSH-trapped metabolites were revealed as the major peaks in the processed LC/MS profiles. Such profiles allowed for comprehensive and reliable identification of these metabolites without the need for any presumptions regarding their behavior or properties with respect to mass spectrometric detection. The algorithm was shown to provide superior results when compared to several commercially available background-subtraction algorithms. Many of the metabolites detected were doubly charged species which would be difficult to detect with traditional GSH adduct screening techniques, and thus, some of the adducts have not previously been reported in the literature.

5-HT1A receptor agonist properties of antipsychotics determined by [35S]GTPgammaS binding in rat hippocampal membranes

1. 5-Hydroxytryptamine 1A (5-HT1A) receptors have attracted increasing attention as a promising target for antipsychotic therapy. Although many atypical antipsychotic drugs, including the prototype clozapine, have been reported to be partial agonists at 5-HT1A receptors, these results are often fragmental and derived mainly from experiments that used cultured cells. 2. In the present study, [35S]guanosine 5'-O-(3-thiotriphosphate) ([35S]GTPgammaS) binding assay in rat hippocampal membranes was applied to a series of antipsychotic drugs, especially atypical antipsychotics. 3. Most, but not all, of atypical antipsychotic drugs and the classical antipsychotic drug nemonapride behaved as partial agonists at 5-HT1A receptors with varied potencies and relative efficacies. The most potent compound was perospirone with a mean EC50 of 27 nmol/L, followed by aripiprazole (45 nmol/L) > ziprasidone (480 nmol/L) > nemonapride (790 nmol/L) > clozapine (3900 nmol/L) > quetiapine (26,000 nmol/L). The maximal percentage increases over the basal binding (%Emax) for these antipsychotic drugs were 30-50%, with the exception of perospirone (approximately 15%), whereas 5-HT stimulated the binding to a mean %Emax of 105%. 4. Increasing concentrations of the selective and neutral 5-HT1A antagonist WAY100635 shifted the concentration-response curve of nemonapride-stimulated [35S]GTPgammaS binding to the right and in parallel. 5. The relative efficacy or intrinsic activity of a compound was affected differently by the differing concentrations of guanosine diphosphate (GDP) in the assay buffer, which should be taken into consideration when determining the relative efficacies of these antipsychotics as 5-HT1A receptor agonists. 6. These results provide important information concerning the relevance of 5-HT1A receptor partial agonist properties in the treatment for schizophrenic patients with most, if not all, of atypical antipsychotic drugs.

Effects of (-)-stepholidine on NMDA receptors: comparison with haloperidol and clozapine

AIM

To examine whether (-)-stepholidine (SPD) has a direct effect on the N-methyl- D-aspartic acid receptors (NMDAR) containing the NMDA receptor subunits NR2A or NR2B and to compare its effect with those of haloperidol (Hal) and clozapine (Cloz).

METHODS

NMDAR was transiently expressed in human embryonic kidney 293 (HEK293) cells. Changes in intracellular calcium concentration ([Ca2+]i) induced by NMDAR activation were monitored with Fura-2 ratio imaging techniques.

RESULTS

SPD had no significant effects on either subunit of NMDAR at a concentration of less than 100 micromol/L. Hal selectively inhibited NMDAR containing the NR2B subunit, whereas Cloz inhibited both subunits of NMDAR. Although both Hal and Cloz inhibited NR1a/NR2B receptor-mediated Ca2+ influx, their effects were different. Hal was more potent and had a faster peak effect than Cloz.

CONCLUSION

Both Hal and Cloz inhibit NMDAR-mediated function, whereas SPD produced only a little inhibition at a high concentration. Based on our other studies, the modulation of SPD on NMDAR function may be via D1 receptor action underlying an indirect mechanism.

Prevalence and nature of side effects during clozapine maintenance treatment and the relationship with clozapine dose and plasma concentration

Clozapine is associated with non-neurological side effects that can be subjectively unpleasant and/or clinically serious. We sought to: (i) assess the nature and prevalence of side effects experienced by patients receiving maintenance treatment with clozapine and (ii) explore the relationship between clozapine plasma concentration and side effect burden. Patients were receiving clozapine maintenance treatment. Open questioning followed by systematic enquiry using the Antipsychotic Non-neurological Side Effects Rating Scale were used to assess side effects. Trough plasma clozapine and norclozapine concentrations were measured. One hundred and three patients participated. On open questioning, 61 patients reported a total of 117 side effects, whereas systematic enquiry identified an additional 649 side effects, with each patient reporting at least one. Clozapine plasma concentrations were significantly but weakly correlated with total Antipsychotic Non-neurological Side Effects Rating Scale score (Pearson correlation=0.29, P<0.004). Patients with a plasma clozapine concentration >0.25 mg/l were significantly more likely to have moderate/severe side effects than patients with lower plasma concentrations (63/76 vs. 12/23, chi=9.07, d.f.=1, P<0.01). The side-effect burden associated with maintenance clozapine treatment is high and the true extent can only be ascertained by systematic inquiry. The use of target plasma concentrations below those used for acute treatment should be explored as a strategy for minimizing side effects.

An in vitro approach to potential methadone metabolic-inhibition interactions

OBJECTIVE

The aim of this study was to assess the drug interaction potential of psychotropic medication on methadone N-demethylation using cDNA-expressed cytochrome P450 CYP enzymes.

METHODS

Methadone was incubated with various drugs (n = 10) and cDNA-expressed CYP3A4, CYP2D6, CYP2B6, CYP2C19 and CYP1A2 enzymes to screen for their inhibition potency. The nature of enzyme selective activity for inhibition was further investigated for potent inhibitors. To test for a mechanism-based component in inhibition, all substances were tested with preincubation and without. 2-Ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) concentration was determined by liquid chromatography/tandem mass spectrometry following liquid/liquid extraction.

RESULTS

Formation of EDDP was catalysed by CYP3A4, CYP2D6 and CYP2C19. The N-demethylation of methadone was preferentially inhibited by amitriptyline, buprenorphine, methylenedioxymethamphetamine (MDMA) and zolpidem. Both amitriptyline and buprenorphine were strong, reversible inhibitors of CYP3A4. Similarly, amitriptyline and MDMA were identified as inhibitors of CYP2D6. Zolpidem revealed a mechanism-based inhibition of CYP3A4.

CONCLUSION

Amitriptyline, MDMA and zolpidem are likely to slow down conversion of methadone and to increase its area under the curve (AUC). A consideration of the in vitro evidence of drug-methadone interactions should help to improve patient care during methadone maintenance treatment.

Pharmacology of N-desmethylclozapine

Currently available treatments for schizophrenia have limited efficacy and are generally poorly tolerated. However, among these antipsychotic agents, clozapine stands apart in having generally superior motoric tolerability and efficacy. One intriguing possibility, based on clinical correlations, receptor activity profiles and studies with animal models predictive of antipsychotic or cognitive action is that the activity of N-desmethylclozapine (NDMC), a major metabolite of clozapine, may, at least in part, underlie the unique efficacy of clozapine. In this review we compare the pharmacological properties of NDMC to those of clozapine and consider how they may contribute to the overall clinical properties of clozapine. We also consider whether NDMC, in its own right, might be a superior antipsychotic drug.

Impaired Microsomal Oxidation of the Atypical Antipsychotic Agent Clozapine in Hepatic Steatosis

Hepatic lipid infiltration (steatosis) is a complication of the metabolic syndrome and can progress to nonalcoholic steatohepatitis and severe liver injury. Microsomal cytochrome P450 (P450) drug oxidases are down-regulated in experimental steatosis. In this study we evaluated the separate and combined effects of lipid accumulation and P450 down-regulation on the microsomal oxidation of the antipsychotic agent clozapine (CLZ), the use of which is associated with an increased incidence of the metabolic syndrome. Several important drug oxidizing P450s were down-regulated, and the formation of N-desmethyl-CLZ (norCLZ) and CLZ N-oxide was decreased in microsomal fractions from orotic acid-induced early steatotic rat liver. Inclusion of lipids extracted from steatotic, but not control, liver decreased the free concentration of CLZ in microsomes and suppressed norCLZ formation; CLZ N-oxidation was unchanged. Triglycerides increased in steatotic liver to 15-fold of control, whereas increases in the monounsaturated oleic acid to 10-fold of control and total polyunsaturated and saturated fatty acids to 4- and 5-fold of control also occurred. Addition of triglycerides containing esterified omega-6 and omega-3 fatty acids inhibited the microsomal formation of norCLZ but not that of CLZ N-oxide; triglycerides esterified with unsaturated and monounsaturated fatty acids were inactive. Thus, drug oxidation may be suppressed in steatosis by P450 down-regulation and the accumulation of polyunsaturated fatty esters. In contrast, the activity of the flavin-containing monooxygenase that mediates CLZ N-oxidation was unimpaired. Lipid deposition in livers of patients with the metabolic syndrome may necessitate dosage adjustments for toxic drugs, including CLZ.

Designer receptors for every body

Using a directed evolution approach, researchers demonstrate a way of creating 'designer' receptors that are specifically activated by a ligand with no other biological activity in the cell.

Synthesis and biodistribution of 8-iodo-11-(4-methylpiperazino)-5H-dibenzo[b,e][1,4]-diazepine: Iozapine

8-Iodo-11-(4-methylpiperazino)-5H-dibenzo[b,e][1,4]-diazepine: Iozapine, a potential D(4)-receptor ligand was synthesized using oxidative iodo-destannylation reaction. The preliminary biodistribution studies of radioiodinated iozapine have shown that the compound is taken up in the brains of mice and rabbits.

Effect of Adjunctive Lamotrigine Treatment on the Plasma Concentrations of Clozapine, Risperidone and Olanzapine in Patients With Schizophrenia or Bipolar Disorder

The effect of lamotrigine on the steady-state plasma concentrations of the atypical antipsychotics clozapine, olanzapine, and risperidone was investigated in patients with schizophrenia or bipolar disorder stabilized on chronic treatment with clozapine (200-500 mg/day; n = 11), risperidone (3-6 mg/day; n = 10) or olanzapine (10-20 mg/day; n = 14)). Lamotrigine was titrated up to a final dosage of 200 mg/day over 8 weeks, and pharmacokinetic assessments were made at baseline and during treatment weeks 6 and 10, at lamotrigine dosages of 100 and 200 mg/day respectively. The plasma concentrations of clozapine, norclozapine, risperidone, and 9-hydroxy-risperidone did not change significantly during treatment with lamotrigine. The mean plasma concentrations of olanzapine were 31 +/- 7 ng/mL at baseline, 32 +/- 7 ng/mL at week 6, and 36 +/- 9 ng/mL at week 10, the difference between week 10 and baseline being statistically significant (P < 0.05). Adjunctive lamotrigine therapy was well tolerated in all groups. These findings indicate that lamotrigine, at the dosages recommended for use as a mood stabilizer, does not affect the plasma levels of clozapine, risperidone, and their active metabolites. The modest elevation in plasma olanzapine concentration, possibly due to inhibition of UGT1A4-mediated olanzapine glucuronidation, is unlikely to be of clinical significance.

No evidence for binding of clozapine, olanzapine and/or haloperidol to selected receptors involved in body weight regulation

The underlying mechanisms of antipsychotic (AP)-induced weight gain are unknown, but both central and peripheral AP target receptors could potentially be involved. This study used radioligand binding assays to compare the binding affinities of clozapine, olanzapine and haloperidol for candidate receptors potentially involved in AP-induced weight gain. Selected candidates derived from known pathways involved in body weight regulation included receptors classified as anorexigenic (bombesin receptor subtype 3, calcitonin gene-related peptide receptor, cholecystokinin receptor, melanocortin-4 receptor, neurotensin receptor 1) or orexigenic (cannabinoid receptor 1, galanin 1 receptor, melanin-concentrating hormone receptor (MCHR), neuropeptide Y1 receptor) as well as receptors involved in physiological actions related to digestion and fluid homeostasis (angiotensin II type 1 receptor, bradykinin B2 receptor, endothelin receptor, neurokinin 1 receptor, vasoactive intestinal polypeptide receptor 1). Clozapine, olanzapine and haloperidol exhibited negligible affinities to all of these receptors except for the MCHR (Ki=501 nM; haloperidol). With respect to other candidates from (neuro)transmitter systems already suggested to be involved in AP-induced weight gain, the binding profile of olanzapine resembled that of clozapine, with high affinity (Ki<10 nM) for serotonin (5-HT) 5-HT2A, 5-HT2C and 5-HT6, muscarinic M1 and histamine H1 receptors. In contrast, the binding profile of haloperidol was substantially different (high affinity only for the dopamine D1 receptor). In conclusion, we have not identified a novel binding site of the two investigated atypical AP that could contribute to the induced weight gain.

Competitive displacement of clozapine from plasma proteins in normolipidemic and hyperlipidemic plasma samples: clinical implications

OBJECTIVE

This study assesses whether competitive displacement of clozapine by warfarin affects clozapine's overall plasma distribution.

METHODS

Warfarin sodium was preincubated in normolipidemic and hyperlipidemic plasma samples in varying concentrations. Following the preincubation with warfarin, [3H]clozapine mixed with unlabeled clozapine was added to the plasma samples. The plasma was separated into its lipoprotein and lipoprotein-deficient fractions by density gradient ultracentrifugation, and clozapine distribution was determined.

RESULTS

When normolipidemic plasma was preincubated with various concentrations of warfarin, no significant redistribution of clozapine was noted among the various plasma lipoprotein fractions. However, in the case of the hyperlipidemic plasma, preincubating with warfarin did result in a significant redistribution of clozapine from the lipoprotein-deficient fraction to the very-low-density and low-density fractions of lipoproteins. Based on pharmacokinetic principles, the steady-state unbound concentration of clozapine in normolipidemic and hyperlipidemic plasma is not expected to change.

CONCLUSION

Although no change in the steady-state unbound (active) concentration of clozapine would predict no change in clinical status, it is possible that this may only apply to the individuals with a normal lipid profile. We believe clozapine's association with lipoproteins (particularly triglycerides) may actually increase clozapine's effectiveness.

Clozapine binds preferentially to cortical D1-like dopamine receptors in the primate brain: a PET study

RATIONALE

The D1-like dopamine receptors have been suggested to play a role in the pathophysiology and treatment of schizophrenia. Previous positron emission tomography studies have demonstrated that the atypical antipsychotic clozapine occupies D1-like dopamine receptors in the striatum in clozapine-treated patients.

OBJECTIVES

The aim of the present study was to compare striatal and cortical D1-like dopamine receptor occupancy by clozapine in the primate brain.

METHODS

Three monkeys were each examined three times at the same day with the radioligand (+)-[11C]NNC 112. The first measurement was at baseline conditions, the second after 1.5 mg/kg and the third after 6 mg/kg clozapine IV. To compare regional levels of nonspecific binding in brain regions, an additional monkey was examined using the inactive enantiomer (-)-[11C]NNC 112. Receptor occupancy was calculated using both the equilibrium-ratio analysis and the simplified reference tissue model.

RESULTS

After 1.5 mg/kg the D1-like dopamine receptor occupancy ranged from 30 to 38% in the striatum, whereas the range was 51 to 57% in the frontal cortex. After 6.0 mg/kg the occupancy was 53 to 64% in the striatum and 63 to 83% in the frontal cortex. The differences between striatal and cortical D(1)-like receptors occupancy were between 12 and 25%. The study with (-)-[11C]NNC 112 did not show regional differences in nonspecific binding that might explain the regional differences in occupancy.

CONCLUSIONS

The higher D1-like dopamine receptor occupancy in the frontal cortex may reflect a different distribution of the D1 and D5 dopamine receptor subtypes among brain regions and different affinity of clozapine for the two subtypes. The finding supports the suggestion that binding to D1-like dopamine receptors may explain clozapine's atypical drug actions.

A Semiquantitative Method for the Determination of Reactive Metabolite Conjugate Levels in Vitro Utilizing Liquid Chromatography−Tandem Mass Spectrometry and Novel Quaternary Ammonium Glutathione Analogues

An in vitro semiquantitative reactive metabolite detection assay is described that incorporates NADPH-supplemented human liver microsomes, a novel quaternary ammonium glutathione analogue conjugating agent (QA-GSH), and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for detection. The assay was developed to have high sample capacity and the potential for high sample throughput. MS/MS detection is selective and sensitive for the QA-GSH conjugating agent and semiquantitation of QA-GSH-reactive metabolite conjugates is performed using QA-GSH standards added to samples prior to analysis [i.e., internal standards (ISs)]. The reactive metabolite trapping capability of the free thiol group in QA-GSH was assessed using model drugs acetaminophen, clozapine, and flutamide, which are bioactivated to afford reactive metabolites. MS signal responses of equimolar amounts of QA-GSH standards were compared to assess the feasibility of using a QA-GSH IS approach to semiquantify reactive metabolite levels in vitro. The full scan Q1 MS response for each standard was within 3.3-fold of one another even though the "parent" moiety structure of each QA-GSH conjugate standard differed significantly. Standard curve analysis using selected reaction monitoring for each QA-GSH standard gave slope values that differed by only 1.5-fold. The QA-GSH IS semiquantitation method was tested by determining the level of QA-GS-acetaminophen conjugate formation at three different concentrations of acetaminophen and comparing the results to those from linear regression of authentic standards. The calculated levels of conjugate formed compared closely with those calculated from linear regression data of authentic standard curves. These results show that the QA-GSH semiquantitation assay described herein is a viable method for semiquantitatively assessing the bioactivation potential in vitro and is well-suited for use in early drug discovery high throughput screening paradigms.

A comparison of the covalent binding of clozapine, procainamide, and vesnarinone to human neutrophils in vitro and rat tissues in vitro and in vivo

Covalent binding of drug reactive metabolites to neutrophils or their precursors is thought to play a role in the development of drug-induced agranulocytosis. In this study, we used immunochemical techniques to compare the covalent binding of clozapine, vesnarinone, and procainamide (three drugs associated with agranulocytosis) to phorbol-12,13-myristate acetate (PMA)-activated human neutrophils in vitro and rat tissues in vivo. In PMA-activated human neutrophils in vitro, clozapine and procainamide modified neutrophil proteins with molecular masses ranging from 30 to 200 kDa, while vesnarinone predominately formed adducts with molecular masses greater than 70 kDa. All three drugs formed adducts at 126, 98, and 58 kDa, and they all covalently bound to human myeloperoxidase when incubated with this enzyme and H2O2 in vitro. Covalent binding to PMA-activated neutrophils was inhibited by nucleophiles, such as glutathione and N-acetylcysteine, but not by N-acetyllysine. In the presence of the PMA, all three drugs covalently bound to activated rat bone marrow cells in vitro, while in its absence only clozapine did. Covalently modified liver proteins were observed in rats treated for 6 weeks with clozapine (25 or 50 mg/kg/day), vesnarinone (300 mg/kg/day), or procainamide (50 mg/kg/day). Clozapine extensively modified proteins in all subcellular fractions; procainamide formed a 99 kDa adduct in a membrane-containing fraction and 57, 47, and 36 kDa adducts in a cytosolic fraction, while vesnarinone formed liver-protein adducts with molecular masses of 82, 62, 49, and 40 kDa in membrane, cytosolic, and S9 fractions. In addition, clozapine and procainamide, but not vesnarinone, formed a 49 kDa drug-protein adduct in the bone marrow of treated rats. Furthermore, procainamide covalently bound to a 58 kDa protein in neutrophils of a patient treated with the drug. We suspect that covalent modification of common targets in the neutrophils by these three drugs plays a role in the development of drug-induced agranulocytosis.

Evaluation of the role of P-glycoprotein in the uptake of paroxetine, clozapine, phenytoin and carbamazapine by bovine retinal endothelial cells

Expression of the drug transport proteins, including P-glycoprotein (Pgp), in the brain vascular endothelium represents a challenge for the effective delivery of drugs for the treatment of several central nervous system (CNS) disorders including depression, schizophrenia and epilepsy. It has been hypothesized that Pgp plays a major role in drug efflux at the blood-brain barrier, and may be an underlying factor in the variable responses of patients to CNS drugs. However, the role of Pgp in the transport of many CNS drugs has not been directly demonstrated. To explore the role of Pgp in drug transport across an endothelial cell barrier derived from the central nervous system, the expression and activity of Pgp in bovine retinal endothelial cells (BRECs) and the effects of representative CNS drugs on Pgp activity were examined. Significant Pgp expression in BRECs was demonstrated by western analyses, and expression was increased by treatment of the cells with hydrocortisone. Intracellular accumulation of the well-characterized Pgp-substrate Taxol was markedly increased by the non-selective transporter inhibitor verapamil and the Pgp-selective antagonist PGP-4008, demonstrating that Pgp is active in these endothelial cells. In contrast, neither verapamil nor PGP-4008 affected the intracellular accumulation of [3H]paroxetine, [14C]phenytoin, [3H]clozapine or [14C]carbamazapine, indicating that these drugs are not substrates for Pgp. Paroxetine, clozapine and phenytoin were shown to be Pgp inhibitors, while carbamazapine did not inhibit Pgp at any concentration tested. These results indicate that Pgp is not likely to modulate patient responses to these drugs.

Intrinsic efficacy of antipsychotics at human D2, D3, and D4 dopamine receptors: identification of the clozapine metabolite N-desmethylclozapine as a D2/D3 partial agonist

Drugs that antagonize D2-like receptors are effective antipsychotics, but the debilitating movement disorder side effects associated with these drugs cannot be dissociated from dopamine receptor blockade. The "atypical" antipsychotics have a lower propensity to cause extrapyramidal symptoms (EPS), but the molecular basis for this is not fully understood nor is the impact of inverse agonism upon their clinical properties. Using a cell-based functional assay, we demonstrate that overexpression of Galphao induces constitutive activity in the human D2-like receptors (D2, D3, and D4). A large collection of typical and atypical antipsychotics was profiled for activity at these receptors. Virtually all were D2 and D3 inverse agonists, whereas none was D4 inverse agonist, although many were potent D4 antagonists. The inverse agonist activity of haloperidol at D2 and D3 receptors could be reversed by mesoridazine demonstrating that there were significant differences in the degrees of inverse agonism among the compounds tested. Aripiprazole and the principle active metabolite of clozapine NDMC [8-chloro-11-(1-piperazinyl)-5H-dibenzo [b,e] [1,4] diazepine] were identified as partial agonists at D2 and D3 receptors, although clozapine itself was an inverse agonist at these receptors. NDMC-induced functional responses could be reversed by clozapine. It is proposed that the low incidence of EPS associated with clozapine and aripiprazole used may be due, in part, to these partial agonist properties of NDMC and aripiprazole and that bypassing clozapine blockade through direct administration of NDMC to patients may provide superior antipsychotic efficacy.

Prediction of clozapine metabolism by on-line electrochemistry/liquid chromatography/mass spectrometry

Combining electrochemical conversion, liquid chromatography and electrospray ionization mass spectrometry (EC/LC/ESI-MS) on-line allows the rapid identification of possible oxidation products of clozapine (CLZ) in the absence and in the presence of glutathione. CLZ is, depending on the applied potential, oxidized to various products in an electrochemical flow-through cell using a porous glassy carbon working electrode. Several hydroxylated and demethylated species are detected on-line using LC/MS. While hydroxy-CLZ is most abundant at a potential of 400 mV, demethylation occurs more readily at higher potentials (at around 700 mV versus Pd/H(2) reference). In the presence of glutathione (GSH), various isomeric glutathione adducts and respective products of further oxidation can be identified. The thioadducts are characterized by tandem MS. Mono-GSH and bis-GSH derivatives can be seen in the chromatograms. The results correlate well with the cyclic voltammetric profile of CLZ. The data are relevant from a pharmacological point of view, since similar metabolites (phases I and II) have been reported in the literature. The EC/LC/MS and EC/MS methods should be valuable tools that can be used to anticipate and understand the metabolization patterns of molecules of pharmacological interest and to point out reactive intermediates.

Dopamine receptor microdomains involved in molecular recognition and the regulation of drug affinity and function

A cationic protonatable amine moiety on dopaminergic ligands forms a high affinity reinforced ionic bond with an anionic aspartic acid at position 3.32 of dopamine receptors. When present, catechol hydroxyls of the ligands form hydrogen bonds with serines at position 5.42, 5.43, and 5.46, and this network of hydrogen bonds serves to orient ligands in the binding-site crevice and increase their binding affinity. A steric clash between aromatic moieties of the ligands and aromatic amino acids of the receptor (e.g., H6.55, F6.52 or F6.51 and W6.48) is likely to be propagated in domino-like fashion along the length of TM6, which is believed to trigger activation of the receptor. Specifically, it is the change in the conformation of W6.48 from an orientation perpendicular to the plane of the lipid membrane to one that is parallel that is believed to result in activation. Molecular determinants that mediate the D4/D2-selectivity of many extremely D4-selective 1,4-DAP ligands, include a nonconserved cluster of bulky amino acids at the TM2/TM3 interface (positions 2.61, 3.28 and 3.29).

N-desmethyl clozapine as purging agent of leukemic cells in vitro

Attempts have been made to improve the results of autologous transplant in leukemia by purging strategies to deplete malignant cells. Clozapine is an atypical antipsychotic agent, which has been associated with hematopoietic toxicity. It has been shown that N-desmethyl clozapine a metabolite of clozapine is toxic to the hematological precursors. There is also evidence that this toxicity is confined to precursors and does not affect hematopoietic stem cells. The metabolite of clozapine (N-desmethyl clozapine) has been found to be more toxic than clozapine itself. This suggests that perhaps this metabolite can be used for purging of leukemic cells. Here it is being hypothesized that N-desmethyl clozapine could be used as an in vitro purging agent for leukemia patients. This might improve the therapeutic efficacy of autologous transplantation in leukemic patients.

Glutamatergic drugs for schizophrenia: a systematic review and meta-analysis

OBJECTIVE

To evaluate the efficacy of glutamatergic drugs, acting agonistically on the N-methyl-D-aspartate (NMDA) or the non-NMDA receptors, in schizophrenia.

METHOD

All relevant randomized controlled trials of glutamatergic drugs for schizophrenia were obtained from the Cochrane Schizophrenia Group's Register of Trials without any language or year limitations. Trials were classified according to their methodological quality. For binary and continuous data, relative risks and weighted (WMD) or standardized mean differences (SMD) were calculated, respectively.

RESULTS

Eighteen short-term trials with 343 randomized patients were included in the meta-analysis. In all of these trials, glycine, D-serine, D-cycloserine or ampakine CX516 was used to augment antipsychotics. NMDA receptor co-agonists glycine and D-serine are effective in reducing negative symptoms (N = 132, fixed effect model SMD = -0.66, 95% CI -1.02 to -0.29, p = 0.0004) of schizophrenia, the magnitude of the effect is moderate. D-Cycloserine, a partial agonist of NMDA receptors, is less effective towards negative symptoms (N = 119, fixed effect model SMD = -0.11, 95% CI -0.48 to 0.25, p = 0.6). Positive symptoms fail to respond to glutamatergic medication. Available derived data on cognitive functioning do not indicate a significant effect of glycine or D-serine (N = 80, random effect model WMD = -2.79, 95% CI -6.17 to 0.60, p = 0.11).

CONCLUSIONS

In the current limited data set, a moderate amelioration of negative symptoms of schizophrenia was found, but no other statistically significant beneficial effects on symptoms of schizophrenia.

Rapid detection and characterization of minor reactive metabolites using stable-isotope trapping in combination with tandem mass spectrometry

Stable-isotope trapping combined with mass spectrometry (MS) neutral loss scanning has recently been developed as a high-throughput method for the in vitro screening of major reactive metabolites. In fact, detection and identification of minor reactive metabolites are equally important since the minor metabolites, even though at low levels, may be highly reactive and also play an important role in drug-induced adverse reactions. In this study, 2-acetylthiophene, clozapine, troglitazone and 7-methylindole were selected as model compounds to further validate the advantages of this method for rapid detection and structural characterization of minor glutathione (GSH) adducts derived from reactive metabolites. The utility of the current method was clearly demonstrated by successful identification of novel reactive metabolites at low levels and also minor ones either masked by non-specific responses or co-eluted with other conjugates. In comparison with existing methods, this method is sensitive, efficient, and suitable for rapid screening and more complete profiling of reactive metabolites.

Adjunctive fluvoxamine inhibits clozapine-related weight gain and metabolic disturbances

BACKGROUND

Adjunctive fluvoxamine inhibits clozapine metabolism and decreases plasma norclozapine (a toxic metabolite of clozapine) to clozapine ratios. This study aimed to demonstrate the effects of fluvoxamine on clozapine-related weight gain, hyperglycemia, and lipid abnormalities.

METHOD

Sixty-eight treatment-resistant inpatients with a DSM-IV diagnosis of schizophrenia were randomly assigned to 2 treatment groups for 12 weeks. The monotherapy group (N = 34) received clozapine (< or = 600 mg/day). The coadministration group (N = 34) received fluvoxamine (50 mg/day) plus low-dose clozapine (< or = 250 mg/day). The study was conducted from August 1999 to October 2002.

RESULTS

The 2 groups were similar in demographic data; baseline body weight and body mass index (BMI); baseline serum glucose, triglyceride, and cholesterol levels; and steady-state plasma clozapine concentration. The monotherapy patients (but not the coadministration patients) had significantly higher (p < .05) body weight, BMI, and serum glucose and triglyceride levels after treatment than at baseline. At week 12, the monotherapy patients also had significantly higher glucose (p = .035), triglyceride (p = .041), and norclozapine (p = .009) (and numerically higher cholesterol) levels than the cotreatment patients. The changes in weight and serum glucose and triglyceride levels were significantly correlated (p = .026, p = .005, and p = .028, respectively) with the plasma concentration of norclozapine but not with plasma levels of clozapine.

CONCLUSION

These results suggest that fluvoxamine cotreatment can attenuate weight gain and metabolic disturbances in clozapine-treated patients. Plasma levels of norclozapine, but not clozapine, are associated with increases in weight and serum glucose and triglyceride levels. Of note, coadministration of fluvoxamine could increase plasma clozapine levels markedly and carry the risk of adverse events. If this combined treatment is applied, conservative introduction with reduced clozapine dosage and careful therapeutic drug monitoring of clozapine concentration is recommended.

Potential clozapine target sites on peripheral hematopoietic cells and stromal cells of the bone marrow

The antipsychotic drug clozapine, acts via interaction with selective neurotransmitter receptor systems. Its use however, is associated with life-threatening agranulocytosis. The mechanism by which this occurs and its possible relationship with the drug's atypicality remain unclear. As a first step in identifying mechanistic pathways involved, profiling of neurotransmitter receptors on human neutrophils, mononuclear and bone marrow stromal cells as putative targets for clozapine-mediated toxicity was undertaken. Expression of mRNA encoding dopaminergic d2, d3, d4; serotonergic 5ht2a, 5ht2c, 5ht3, 5ht6, 5ht7; adrenergic alpha1a, alpha2; histaminergic h1 and muscarinic m1, m2, m3, m4, m5 receptors was analyzed by reverse transcription-polymerase chain reaction methods. While 5ht2c, 5ht6, m1 and m2 mRNA were undetected, the presence of the other receptors indicates sites at which clozapine could bind and induce toxicity of neutrophils and stromal components which regulate granulopoiesis. The functional significance of differential receptor expression while unknown, may argue for neural regulation of hematopoiesis.

Effects of clozapine and its metabolites on the 5-HT2 receptor system in cortical and hippocampal cells in vitro

PURPOSE

The goal of the present study was to determine the effects of clozapine (Cloz) and its metabolites norclozapine (Norcloz) and clozapine-N-oxide (Cloz-N-oxide) on the 5-HT(2) receptor system on the levels of protein and gene expression in in vitro systems of primary cortical cells of the rat and human hippocampal SHS5Y5 neuroblastoma cells.

METHODS

Clinically relevant concentrations of Cloz (200/400 ng/ml) and its metabolites (200 ng/ml) were used for the examination of the effects of Cloz and its metabolites on serotoninergic 5-HT(2) receptor parameters (density, affinity and mRNA levels) as well as on glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA levels in primary cortical cells of the rat after treatment for 24 h under in vitro conditions. To compare the results to human cells, we also measured treatment-induced changes in 5-HT(2) and GAPDH mRNA levels in human hippocampal SHS5Y5 cells.

RESULTS

A significant decrease was found in primary cortical cells for 5-HT(2) receptor density (Cloz 200/Cloz 400/Norcloz 200 and Cloz-N-oxide 200 vs. control) and 5-HT(2A) receptor mRNA levels (Cloz 200 vs. control). 5-HT(2A) receptor mRNA levels were also significantly reduced (Norcloz 200 vs. control) in SHS5Y5 cells. GAPDH mRNA levels were not affected.

CONCLUSIONS

The results of the present study show that Cloz and Norcloz induce significant alterations on the 5-HT(2) receptor system in primary cortical cells of the rat and in human hippocampal cells.

Characterisation of Gs activation by dopamine D1 receptors using an antibody capture assay: antagonist properties of clozapine

Herein, we examined the direct coupling of human dopamine D1 receptors to G(s) proteins using an antibody capture assay together with a detection technique employing scintillation proximity assay beads. Using a specific antibody, dopamine (DA) and the selective dopamine D1 receptor agonists, 6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SKF81297) and 3-allyl-6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SKF82958), behaved as high-efficacy agonists ( approximately 100%) in stimulating guanosine-5'-O-(3-[35S]thio)-triphosphate ([35S]GTP gamma S) binding to G(s) in L-cells, whereas 2,3,4,5,-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine (SKF38393) displayed partial agonist properties (70%). The action of dopamine was specifically mediated by human dopamine D1 receptors inasmuch as the selective human dopamine D1 receptor antagonist, (R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-benzazepine-7-ol (SCH23390), blocked dopamine-induced [35S]GTP gamma S binding to G(s) with a pK(B) (9.29) close to its pK(i) (9.33). The antipsychotic agents, clozapine and haloperidol, displayed no intrinsic activity when tested alone and inhibited dopamine-stimulated G(s) activation with pK(B)'s of 6.7 and 7.3, respectively, values close to their pK(i) values at these sites. In conclusion, the use of an anti-G(s) protein immunoprecipitation assay coupled to scintillation proximity assays allows direct evaluation of the functional activity of dopamine D1 receptors ligands at the G protein level. Employing this novel technique, the typical and atypical antipsychotics, clozapine and haloperidol, respectively, both exhibited antagonist properties at dopamine D1 receptors.