Karuna Jayathilake

The role of M1 muscarinic receptor agonism of N-desmethylclozapine in the unique clinical effects of clozapine

RationaleClozapine is a unique antipsychotic, with efficacy against positive symptoms in treatment-resistant schizophrenic patients, and the ability to improve cognition and treat the negative symptoms characteristic of this disease. Despite its unique clinical actions, no specific molecular mechanism responsible for these actions has yet been described.Objectives and methodsTo comprehensively profile a large library of neuropsychiatric drugs, including most antipsychotics, at human monoamine receptors using R-SAT, an in vitro functional assay.ResultsProfiling revealed that N-desmethylclozapine (NDMC), the principal metabolite of clozapine, but not clozapine itself, is a potent and efficacious muscarinic receptor agonist, a molecular property not shared by any other antipsychotic. To further explore the role of NDMC muscarinic receptor agonist properties in mediating the physiological actions of clozapine, systemically administered NDMC was found to stimulate the phosphorylation of mitogen-activated protein kinase (MAP kinase) in mouse CA1 hippocampal neurons, an effect that was blocked by scopolamine, confirming central M1 muscarinic receptor agonist activity in vivo. Lastly, an analysis of clozapine and NDMC serum levels in schizophrenic patients indicated that high NDMC/clozapine ratios better predicted improvement in cognitive functioning and quality of life than the levels of either compound alone.ConclusionsThe muscarinic receptor agonist activities of NDMC are unique among antipsychotics, and provide a possible molecular basis for the superior clinical effects of clozapine pharmacotherapy.

A comparison of the effect of clozapine with typical neuroleptics on cognitive function in neuroleptic-responsive schizophrenia

Clozapine has been reported to improve selected aspects of cognitive function in neuroleptic-resistant schizophrenia. In this study, we report the first direct comparison of the effect of clozapine and typical neuroleptic drugs on cognitive function in neuroleptic-responsive schizophrenia. Sixty-four patients with recent onset, neuroleptic-responsive schizophrenia or schizoaffective disorder were randomly assigned to either clozapine (n = 35) or typical neuroleptics (n = 29) and followed for 12 months. They were administered a comprehensive cognitive test battery at baseline and at 6 weeks, 6 months and 12 months after initiating drug treatment. Treatment with clozapine improved psychomotor speed and attention [Digit Symbol Substitution Test (DSST)] and verbal fluency [Category Instance Generation and Controlled Word Association Test (CWAT)] at 6 weeks. The improvement in these measures was maintained throughout the 12-month period. Treatment with typical neuroleptics produced no sustained improvement in any cognitive measure, except for a tendency to improve delayed recall memory (Verbal List Learning Test). The improvement in the DSST and CWAT was significantly greater with clozapine treatment compared to that with typical neuroleptics. These improvements were not related to improvement in psychopathology. These results suggest that clozapine is superior to typical neuroleptics in improving specific types of cognitive function in recent onset, neuroleptic-responsive schizophrenia.

Clozapine-induced weight gain predicts improvement in psychopathology.

BACKGROUND Some, but not all, previous studies have indicated that weight gain is associated with greater improvement in psychopathology during clozapine treatment. Possible reasons for the inconsistent results include failure to adjust for initial body weight and level of psychopathology, differences in trial duration, outcome measures, reliability of assessment, concomitant medications and clozapine dosage. The purpose of this study was to test the hypothesis that clozapine-induced weight gain is related to antipsychotic efficacy at 6 weeks and 6 months after adjusting for initial body weight and severity of illness. METHODS Weight and psychopathology were determined in 74 patients with schizophrenia or schizoaffective disorder at baseline and after 6 weeks and 6 months of open treatment with clozapine monotherapy. The primary measures of psychopathology were the Brief Psychiatric Rating Scale (BPRS) Total and Positive symptoms subscales, Schedule for Assessment of Negative Symptoms (SANS), Schedule for Assessment of Positive Symptoms (SAPS) and Global Assessment of Function Scale (GAFS). RESULTS Significant improvement in the key measures of psychopathology was noted at 6 weeks and 6 months. Mean weight gains at 6 weeks and 6 months were 3.7+/-5.7 S.D. and 7.3+/-7.9 S.D. kg, respectively, with the increase between 6 weeks and 6 months being significant. Age, but not gender, initial body weight, clozapine dosage or plasma levels predicted weight gain at both time points. At 6 weeks and 6 months, after adjustment for age, initial weight and level of psychopathology, the percentage change in weight significantly predicted the improvement in the BPRS Total and Positive symptoms subscale, the SANS Global score, as well as other measures of psychopathology. CONCLUSIONS Increase in weight with clozapine predicted improvement in psychopathology. This suggests that effects of clozapine on neurotransmitters which influence weight gain, e.g. 5-HT(2C) and 5-HT(1a) antagonism, in association with individual variations in these receptors and others molecules, e.g. peptides and transporters, due to polymorphisms or post-translational editing of mRNAs, may also contribute to the improvement in psychopathology.

Occupancy of Striatal and Extrastriatal Dopamine D2 Receptors by Clozapine and Quetiapine

Clozapine and quetiapine have a low incidence of extrapyramidal side effects at clinically effective doses, which appears to be related to their significantly lower occupancy of striatal dopamine D2 receptors (DA D2r) compared to typical antipsychotic drugs (APDs). Animal studies have indicated that clozapine and quetiapine produce selective effects on cortical and limbic regions of the brain and in particular on dopaminergic neurotransmission in these regions. Previous PET and SPECT studies have reported conflicting results regarding whether clozapine produces preferential occupancy of cortical DA D2r. To examine whether clozapine and/or quetiapine produce preferential occupancy of DA D2r in cortex and limbic regions, we studied the occupancy of putamenal, ventral striatal, thalamic, amygdala, substantia nigra, and temporal cortical DA D2r using PET with [18F]fallypride in six schizophrenic subjects receiving clozapine monotherapy and in seven schizophrenic subjects receiving quetiapine monotherapy. Doses were chosen clinically to minimize psychopathology at tolerable levels of side effects such as drowsiness. All had minimal positive symptoms at the time of the study. Regional receptor occupancies were estimated using mean regional DA D2r levels calculated for 10 off-medication schizophrenic subjects. Both clozapine and quetiapine produced lower levels of putamenal DA D2r occupancy than those reported for typical APDs, 47.8 and 33.5%, respectively. Clozapine produced preferential occupancy of temporal cortical vs putamenal DA D2r, 59.8% (p=0.05, corrected for multiple comparisons), and significantly lower levels of occupancy in the substantia nigra, 18.4% (p=0.0015, corrected for multiple comparisons). Quetiapine also produced preferential occupancy of temporal cortical DA D2r, 46.9% (p=0.03, corrected for multiple comparisons), but did not spare occupancy of substantia nigra DA D2r. The therapeutic effects of clozapine and quetiapine appear to be achieved at less than the 65% threshold for occupancy seen with typical APDs, consistent with the involvement of non-DA D2r mechanisms in at least partially mediating the therapeutic effects of these drugs. Preferential occupancy of cortical DA D2r, sparing occupancy of substantia nigra receptors, and non-DA D2r-mediated actions may contribute to the antipsychotic actions of these and other atypical APDs.

Occupancy of striatal and extrastriatal dopamine D2/D3 receptors by olanzapine and haloperidol.

There have been conflicting reports as to whether olanzapine produces lower occupancy of striatal dopamine D2/D3 receptor than typical antipsychotic drugs and preferential occupancy of extrastriatal dopamine D2/D3 receptors. We performed [18F] fallypride PET studies in six schizophrenic subjects treated with olanzapine and six schizophrenic subjects treated with haloperidol to examine the occupancy of striatal and extrastriatal dopamine receptors by these antipsychotic drugs. [18F] setoperone PET studies were performed in seven olanzapine-treated subjects to determine 5-HT2A receptor occupancy. Occupancy of dopamine D2/D3 receptors by olanzapine was not significantly different from that seen with haloperidol in the putamen, ventral striatum, medial thalamus, amygdala, or temporal cortex, that is, 67.5–78.2% occupancy; olanzapine produced no preferential occupancy of dopamine D2/D3 receptors in the ventral striatum, medial thalamus, amygdala, or temporal cortex. There was, however, significantly lower occupancy of substantia nigra/VTA dopamine D2/D3 receptors in olanzapine-treated compared to haloperidol-treated subjects, that is, 40.2 vs 59.3% (p=0.0014, corrected for multiple comparisons); in olanzapine-treated subjects, the substantia nigra/VTA was the only region with significantly lower dopamine D2/D3 receptor occupancy than the putamen, that is, 40.2 vs 69.2% (p<0.001, corrected for multiple comparison). Occupancy of 5-HT2A receptors was 85–93% in the olanzapine- treated subjects. The results of this study demonstrated that olanzapine does not produce preferential occupancy of extrastriatal dopamine D2/D3 receptors but does spare substantia nigra/VTA receptors. Sparing of substantia nigra/VTA dopamine D2/D3 receptor occupancy may contribute to the low incidence of extrapyramidal side effects in olanzapine-treated patients.

Fluoxetine, but not Tricyclic Antidepressants, Potentiates the 5-Hydroxytryptophan-Mediated Increase in Plasma Cortisol and Prolactin Secretion in Subjects with Major Depression or with Obsessive Compulsive Disorder

It has been suggested that the clinical efficacy of chronic treatment with selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine and perhaps all antidepressants is due to their ability to enhance serotonergic activity. The effects of chronic treatment with fluoxetine or tricyclic antidepressants on the L-5-hydroxytryptophan (200 mg, L-5-HTP; PO)–induced increases in plasma cortisol and prolactin (PRL) concentrations were studied in patients with major depression or obsessive compulsive disorder (OCD). Administration of L-5-HTP increased plasma cortisol and PRL levels in medicated and unmedicated patients with major depression or OCD. The L-5-HTP–induced cortisol and PRL responses were significantly higher in fluoxetine-treated than in tricyclic-treated or unmedicated major depressed patients. The latter two groups did not differ significantly in their cortisol or PRL responses to L-5-HTP. The L-5-HTP–induced increases in cortisol and PRL in fluoxetine-treated patients with major depression or OCD were not significantly different. The results suggest that fluoxetine, but not tricyclic antidepressants, potentiates 5-HT receptor–mediated stimulation of cortisol and PRL secretion in humans, consistent with available evidence that fluoxetine treatment, but not tricyclic antidepressants, increases central serotonergic activity in patients with MD or OCD by a presynaptic mechanism.

The Blunted Plasma Cortisol Response to Apomorphine and Its Relationship to Treatment Response in Patients with Schizophrenia

The adrenocorticotropic hormone (ACTH) and cortisol responses to apomorphine (APO), a direct acting dopamine (DA) agonist, have been reported to be significantly blunted in neuroleptic-free patients with schizophrenia (SCH). This study primarily examined the cortisol, but also the prolactin (PRL) and growth hormone (GH), response to APO in patients with SCH compared to normal controls, as well as the relationship between endocrine measures and response to antipsychotic drug treatment. APO, 0.01 mg/kg, or placebo was administered to 51–98 patients with SCH and 15–25 normal controls. Psychopathology was assessed at the baseline and six weeks after drug treatment. The plasma cortisol response to APO was markedly blunted in patients with SCH compared to normal controls. Patients who responded to six weeks of treatment with antipsychotic drugs had a higher cortisol response to APO compared to non-responders. The plasma GH, but not PRL, response to APO was blunted in male patients with SCH. Neither plasma GH nor PRL responses to APO were related to treatment response at six weeks. These results provide further evidence of dopaminergic dysfunction in SCH. Furthermore, the APO-stimulated cortisol response may be predictive of subsequent clinical response to antipsychotic drug treatment.

Effects of subchronic treatment with valproate on L-5-HTP-induced cortisol responses in mania: evidence for increased central serotonergic neurotransmission

The mechanisms underlying the acute and prophylactic antimanic properties of valproate have remained elusive. There are some reports that treatment with valproic acid may increase brain serotonergic neurotransmission in the rodent. This study was carried out in order to investigate the effects of subchronic therapy with valproate on central serotonin metabolism in manic patients. Toward this end, the authors examined plasma cortisol responses to 200 mg (orally) L-5-hydroxy-tryptophan (L-5-HTP) in 10 manic patients both before and after subchronic treatment with valproate. Administration of L-5-HTP resulted in significantly increased cortisol responses both before and after treatment with valproate. The L-5-HTP-induced cortisol responses were significantly higher after treatment with valproate than before treatment. It is suggested that valproate may increase central serotonergic neurotransmission and that this stimulation may play a role in the antimanic effects of valproate.

No association of the T102C polymorphism of the serotonin 2A receptor gene (HTR2A) with suicidality in schizophrenia.

Additional evidence for a role of serotonin (5-HT) in the pathogenesis of suicidal behavior is provided by a recent report that the 5-HT2A (HTR2A) T102C polymorphism was associated with suicidality in patients with major depression. Three other studies have, however, failed to find an association between this polymorphism and suicidality in major depression. The goal of the present study was to test the association of allele C of T102C HTR2A polymorphism with suicidality in patients with schizophrenia or schizoaffective disorder. Seventy-one patients with DSM-III-R diagnosis of schizophrenia or schizoaffective disorder were included in the study. Patients were genotyped for the T102C HTR2A polymorphism. Information about lifetime suicidality was obtained during the course of SADS interviews. In addition, current suicidality was assessed by the Hamilton Depression Scale in 46 patients. There were no significant differences in allele frequencies and genotype distributions between suicidal and non-suicidal patients using lifetime or current suicidality measures. The results of this study did not demonstrate a robust association of the allele C of the T102C HTR2A polymorphism with lifetime or current suicidality in patients with schizophrenia. However, the mean Hamilton Depression Scale item for current suicidality was significantly higher in patient with genotype T/C compared to those with genotype C/C (p = 0.01) and marginally higher than for the patients with genotype T/T (p=0.06). The relatively small sample size suggests a study with a larger sample and greater power would be of interest.

A randomized trial comparing clozapine and typical neuroleptic drugs in non-treatment-resistant schizophrenia

Clozapine has been shown to be superior to typical neuroleptic drugs for treating positive symptoms in treatment-resistant (TR) schizophrenia. Long-term data from randomized clinical trials comparing clozapine with typical neuroleptics in non-TR schizophrenia are rare. We previously reported that clozapine was superior to typical neuroleptic drugs in some domains of cognition in recent onset non-TR schizophrenia. We now present data on psychopathology and quality of life from this randomized, flexibly dosed, 24-month study of clozapine vs. typical neuroleptics in non-TR schizophrenia patients. Both treatments produced significant improvement in measures of psychopathology, quality of life, and global function, with minor exceptions. There was no difference in extrapyramidal side effects between the patients treated with clozapine or typical neuroleptics. However, significantly more relapse/rehospitalization drop-outs occurred in the typical neuroleptic group. Two patients treated with typical neuroleptics, but none treated with clozapine, became non-responsive to treatment. Clozapine was associated with significantly greater weight gain. Clozapine and typical neuroleptic drugs appear to produce equivalent improvement in psychopathology in patients with non-TR schizophrenia. Clozapine may be more effective than typical neuroleptics for treatment retention and prevention of relapse, but it produces more severe metabolic side effects. These considerations should be taken into account in decisions of how best to utilize clozapine in the treatment of schizophrenia.