Quetiapine and norquetiapine in plasma and cerebrospinal fluid of schizophrenic patients treated with quetiapine: correlations to clinical outcome and HVA, 5-HIAA, and MHPG in CSF

The association between inflammation and kynurenine pathway metabolites in electroconvulsive therapy for schizophrenia: Implications for clinical efficacy

The kynurenine pathway (KP) of tryptophan has been implicated in the pathogenesis of schizophrenia and its interaction with the immune system has been suggested to play a role. In this study, 28 schizophrenia patients and 25 healthy controls were recruited and divided into different inflammatory subgroups using a two-step recursive clustering analysis. Cytokine gene expression and plasma KP metabolites were measured before, during and after treatment. Our findings indicated that schizophrenia patients had lower levels of Tryptophan (TRP), N-formylkynurenine (NFK), xanthinic acid (XA), quinolinic acid (QA), kynurenic acid (KYNA), KYNA/KYN and QA/KYNA, but higher levels of IL-18 mRNA, KYN/TRP compared to healthy controls (all p < 0.05). After electroconvulsive therapy (ECT), patients with low inflammation achieved better clinical improvement (PANSS scores) compared to those with high inflammation (F = 5.672, P = 0.025), especially in negative symptoms (F = 6.382, P = 0.018, η2 = 0.197). While IL-18 mRNA (F = 32.910, P < 0.0001) was significantly decreased following ECT, the KYN/TRP (F = 3.455, p = 0.047) and KYNA/TRP (F = 4.264, P = 0.026) only significantly decreased in patients with low inflammation. Correlation analyses revealed that baseline IL-18 gene expression significantly correlated with pre- (r = 0.537, p = 0.008) and post-KYNA/TRP (r = 0.443, p = 0.034), post-KYN/TRP (r = 0.510, p = 0.013), and post-negative symptoms (r = 0.525, p = 0.010). Moreover, baseline TRP (r = -0.438, p = 0.037) and XA (r = -0.516, p = 0.012) were negatively correlated with baseline PANSS, while post-KYN (r = -0.475, p = 0.022), 2-AA (r = -0.447, p = 0.032) and KYN/TRP (r = -0.566, p = 0.005) were negatively correlated with Montreal Cognitive Assessment (MoCA) following ECT. Overall, these findings suggested that the association between inflammation and kynurenine pathway plays an essential role in mechanism of ECT for schizophrenia and that the regulation of ECT on KP is influenced by inflammatory characteristics, which may relate to clinical efficacy in schizophrenia.

A New Look on an Old Issue: Comprehensive Review of Neurotransmitter Studies in Cerebrospinal Fluid of Patients with Schizophrenia and Antipsychotic Effect on Monoamine's Metabolism

Neurotransmitters metabolism has a key role in the physiopathology of schizophrenia as demonstrated by studies measuring monoamine metabolites in patient’s cerebrospinal fluid (CSF) since the beginning of the antipsychotic use. This comprehensive review aims to understand the anomalies of CSF monoamines in schizophrenia and their correlation with clinical and paraclinical features. We also review the influence of antipsychotic treatment on CSF monoamines and discuss the connection with metabolic and inflammatory processes. Studies comparing CSF homovanillic acid (HVA) levels between patients and controls are miscellaneous, due to the heterogeneity of samples studies. However, low HVA is associated with more positive symptoms and a poorer outcome and negatively correlated with brain ventricle size. Based on humans and animals’ studies, antipsychotic treatments increase HVA during the first week of administration and decrease progressively over the time with a fall-off after withdrawal. 5‐hydroxyindolacetic acetic acid levels do not seem to be different in the patient’s CSF compared to controls. Considering metabolic co-factors of neurotrans-mitters synthesis, there is evidence supporting an increase of kynurenic acid in the CSF of patients with schizophrenia. Few studies explore folate metabolism in CSF. Literature also emphasizes the relationship between folate metabolism, inflammation and monoamine’s metabolism. Those results suggest that the CSF monoamines could be correlated with schizophrenia symptoms and treatment outcome. However, further studies, exploring the role of CSF monoamines as biomarkers of disease severity and response to treatment are needed. They should assess the antipsychotic prescription, inflammatory markers and folate metabolism as potential confounding factors.

Differences in P-glycoprotein activity in human and rodent blood-brain barrier assessed by mechanistic modelling

Variation in the efficacy and safety of central nervous system drugs between humans and rodents can be explained by physiological differences between species. An important factor could be P-glycoprotein (Pgp) activity in the blood–brain barrier (BBB), as BBB expression of this drug efflux transporter is reportedly lower in humans compared to mouse and rat and subject to an age-dependent increase. This might complicate animal to human extrapolation of brain drug disposition and toxicity, especially in children. In this study, the potential species-specific effect of BBB Pgp activity on brain drug exposure was investigated. An age-dependent brain PBPK model was used to predict cerebrospinal fluid and brain mass concentrations of Pgp substrate drugs. For digoxin, verapamil and quinidine, in vitro kinetic data on their transport by Pgp were derived from literature and used to scale to in vivo parameters. In addition, age-specific digoxin transport was simulated for children with a postnatal age between 25 and 81 days. BBB Pgp activity in the model was optimized using measured CSF data for the Pgp substrates ivermectin, indinavir, vincristine, docetaxel, paclitaxel, olanzapine and citalopram, as no useful in vitro data were available. Inclusion of Pgp activity in the model resulted in optimized predictions of their brain concentration. Total brain-to-plasma AUC values (Kp,brain) in the simulations without Pgp were divided by the Kp,brain values with Pgp. Kp ratios ranged from 1 to 45 for the substrates investigated. Comparison of human with rodent Kp,brain ratios indicated ≥ twofold lower values in human for digoxin, verapamil, indinavir, paclitaxel and citalopram and ≥ twofold higher values for vincristine. In conclusion, BBB Pgp activity appears species-specific. An age-dependent PBPK model-based approach could be useful to extrapolate animal data to human adult and paediatric predictions by taking into account species-specific and developmental BBB Pgp expression.

Norquetiapine blocks the human cardiac sodium channel Nav1.5 in a state-dependent manner

Quetiapine, an atypical antipsychotic drug, is used for the treatment of schizophrenia and acute mania. Although a previous report showed that quetiapine blocked hERG potassium current, quetiapine has been considered relatively safe in terms of cardiovascular side effects. In the present study, we used the whole-cell patch-clamp technique to investigate the effect that quetiapine and its major metabolite norquetiapine can exert on human cardiac sodium channels (hNa_v1.5). The half-maximal inhibitory concentrations of quetiapine and norquetiapine at a holding potential of -90 mV near the resting potential of cardiomyocytes were 30 and 6 μM, respectively. Norquetiapine as well as quetiapine was preferentially bound in the inactivated state of the hNa_v1.5 channel. Norquetiapine slowed the recovery from inactivation of hNa_v1.5 and consequently induced strong use-dependent inhibition. Our results indicate that norquetiapine blocks hNa_v1.5 current in concentration-, state- and use-dependent manners, suggesting that the blockade of hNa_v1.5 current by norquetiapine may shorten the cardiac action potential duration and reduce the risk of QT interval prolongation induced by the inhibition of hERG potassium currents.

Plasma monoamines change under dopamine supersensitivity psychosis in patients with schizophrenia: A comparison with first-episode psychosis

BACKGROUND

Patients with first-episode psychosis respond well to initial antipsychotic treatment, but among patients experiencing a relapse of psychosis, the response rate falls to approximately 30%. The mechanism of this discrepancy has not been clarified, but the development of dopamine supersensitivity psychosis with the underlying up-regulation of post-synaptic dopamine D2 receptors could be involved in this lesser response. It is uncertain whether elevated dopamine synthesis and release occurs in patients with dopamine supersensitivity psychosis, in contrast to those with first-episode psychosis.

PATIENTS AND METHODS

We examined a first-episode psychosis group (n=6) and a chronic schizophrenia group, i.e. patients experiencing relapse (n=23) including those who relapsed due to dopamine supersensitivity psychosis (n=18). Following the initiation of treatment, we measured the patients' blood concentrations of homovanillic acid and 3-methoxy-4-hydroxyphenylglycol at two weeks and four weeks after the baseline measurements.

RESULTS

The first-episode psychosis group tended to show decreased homovanillic acid, accompanied by an improvement of symptoms. The chronic schizophrenia group showed no alteration of homovanillic acid or 3-methoxy-4-hydroxyphenylglycol over the treatment period. These results were the same in the dopamine supersensitivity psychosis patients alone.

CONCLUSIONS

Our findings suggest that unlike first-episode psychosis, the release of dopamine from presynaptic neurons did not increase in relapse episodes in the patients with dopamine supersensitivity psychosis. This indirectly indicates that the development of supersensitivity of post-synapse dopamine D2 receptor is involved in relapse in dopamine supersensitivity psychosis patients.

No major influence of regular tobacco smoking on cerebrospinal fluid monoamine metabolite concentrations in patients with psychotic disorder and healthy individuals

Metabolism of the monoamines dopamine, serotonin and noradrenaline, is altered in the central nervous system of people with schizophrenia, and their major metabolites homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol (MHPG), respectively, have been intensively studied as indirect measures of these neurotransmitters in cerebrospinal fluid (CSF). Regular tobacco smoking has been shown to alter neurotransmitter metabolism in the brain and studies have found CSF monoamine metabolite concentrations to be substantially lower in smokers. However, few studies investigating these monoamines in CSF have controlled for regular tobacco smoking. We investigated if regular tobacco smoking influences CSF HVA, 5-HIAA and MHPG concentrations in patients treated for psychotic disorders (n = 69) and healthy non-psychotic human volunteers (n = 200). After lumbar puncture CSF samples were analyzed with mass fragmentography. CSF HVA, 5-HIAA and MHPG concentrations did not significantly differ between smokers and non-smokers neither in patients, nor in healthy subjects, whereas back-length predicted HVA and 5-HIAA and antipsychotic medication MHPG concentrations. The results indicate that regular tobacco smoking has no significant effect on monoamine metabolite concentrations in CSF. This suggests that lack of controlling for regular tobacco smoking should not substantially violate the results in studies of the major monoamine metabolites in CSF.

Cerebrospinal fluid monoamine metabolite profiles in bipolar disorder, ADHD, and controls

Alterations in monoaminergic signaling are suggested as key aspects of the pathophysiology in bipolar disorder and ADHD, but it is not known if the monoamine metabolic profile differs between these disorders. One method to study monoaminergic systems in humans is to measure monoamine end-point metabolite concentrations in cerebrospinal fluid (CSF). Here, we analyzed CSF monoamine metabolite concentrations in 103 adults with bipolar disorder, 72 adults with ADHD, and 113 controls. Individuals with bipolar disorder had significantly higher homovanillic acid (HVA, 264 ± 112 nmol/L, p < 0.001) and 5-hydroxyindoleacetic acid (5-HIAA, 116 ± 42 nmol/L, p = 0.001) concentration, but lower 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG, 38 ± 8 nmol/L, p < 0.001) concentrations than controls (HVA, 206 ± 70 nmol/L; 5-HIAA, 98 ± 31 nmol/L; and MHPG, 42 ± 7 nmol/L). Higher HVA concentrations were associated with a history of psychosis in the bipolar disorder sample. Subjects with ADHD had higher HVA (240 ± 94 nmol/L, p < 0.001) concentrations compared with controls. In addition, SSRI treatment was associated with lower 5-HIAA concentrations in both patient groups. A power analysis indicated that for within-group comparisons, only large effects would be reliably detectable. Thus, there may be moderate-to-small effects caused by medication that were not detected due to the limited size of the sub-groups in these analyses. In conclusion, the present study suggests disorder-specific alterations of CSF monoamine metabolite concentrations in patients with bipolar disorder and ADHD compared with controls; these differences were independent of acute symptoms and medication effects.

Measuring citalopram in blood and cerebrospinal fluid: revealing a distribution pattern that differs from other antidepressants

The aim of this study was to measure blood and cerebrospinal fluid concentrations of citalopram and its weakly active N-demethylated metabolite desmethylcitalopram to account for the distribution between the two compartments. The findings are discussed in the context with own preceding studies on the distribution pattern of different antidepressants. Concentrations of citalopram were measured in blood serum and cerebrospinal fluid of 18 patients treated with daily doses of 10-40 mg. Daily doses were correlated with serum and cerebrospinal fluid concentrations, and serum concentrations were correlated with concentrations in cerebrospinal fluid. Serum concentrations of citalopram and desmethylcitalopram showed no significant correlation to the daily dose, r=0.164, P=0.515, and r=0.174, P=0.505, respectively, whereas citalopram concentrations in serum and cerebrospinal fluid were highly correlated (r=0.763, P<0.001). The cerebrospinal fluid/serum ratio for citalopram (total=bound+unbound concentration) varied between 0.14 and 0.86 (mean 0.35, SD 0.16). By correcting the mean cerebrospinal fluid/serum ratio for 80% plasma protein binding, cerebrospinal fluid concentrations of citalopram were on average 77% higher than the calculated unbound serum concentration with a ratio of 1.77 (SD 0.81, range 0.68-4.29). Findings indicate a very good ability of citalopram to cross the blood-brain and cerebrospinal fluid barrier. High concentrations of citalopram in the cerebrospinal fluid are indicative of active transport of citalopram into or missing active transport out of the cerebrospinal fluid. The results suggest a high ability of citalopram to enter the brain with sufficiently high drug concentrations at the target sites within the brain, contributing toward clinical efficacy.

Associations between a locus downstream DRD1 gene and cerebrospinal fluid dopamine metabolite concentrations in psychosis

Dopamine activity, mediated by the catecholaminergic neurotransmitter dopamine, is prominent in the human brain and has been implicated in schizophrenia. Dopamine targets five different receptors and is then degraded to its major metabolite homovanillic acid (HVA). We hypothesized that genes encoding dopamine receptors may be associated with cerebrospinal fluid (CSF) HVA concentrations in patients with psychotic disorder. We searched for association between 67 single nucleotide polymorphisms (SNPs) in the five dopamine receptor genes i.e., DRD1, DRD2, DRD3, DRD4 and DRD5, and the CSF HVA concentrations in 74 patients with psychotic disorder. Nominally associated SNPs were also tested in 111 healthy controls. We identified a locus, located downstream DRD1 gene, where four SNPs, rs11747728, rs11742274, rs265974 and rs11747886, showed association with CSF HVA concentrations in psychotic patients. The associations between rs11747728, which is a regulatory region variant, and rs11742274 with HVA remained significant after correction for multiple testing. These associations were restricted to psychotic patients and were absent in healthy controls. The results suggest that the DRD1 gene is implicated in the pathophysiology of psychosis and support the dopamine hypothesis of schizophrenia.

Duloxetine enters the brain - But why is it not found in the cerebrospinal fluid

BACKGROUND

Antidepressants enter the brain to reach their site of action in a different extent. However, there has been no study to date about duloxetine's ability to enter the brain and cerebrospinal fluid. Aim of this study was to measure blood and cerebrospinal fluid concentrations of duloxetine and to account for the distribution between the two compartments.

METHODS

Concentrations of duloxetine were measured in blood serum and cerebrospinal fluid of 19 patients treated with daily doses of 30-120mg. Daily doses were correlated with serum and cerebrospinal fluid concentrations and serum concentrations were correlated with concentrations in cerebrospinal fluid.

RESULTS

Serum concentrations of duloxetine showed a moderate but significant correlation with the applied daily dose, r=+0.473, p=0.04. Duloxetine concentrations in the cerebrospinal fluid above the designated limit of quantification of 2.0ng/mL were only found in three of the 19 patients.

CONCLUSIONS AND LIMITATIONS

Contrasting to own preceding studies on venlafaxine, mirtazapine and citalopram with comparably high concentrations in cerebrospinal fluid, the here presented findings indicate that duloxetine shows a very different distribution pattern. Very low concentrations in the cerebrospinal fluid may be due to the fact that the drug crosses the blood-cerebrospinal fluid barrier much worse than other antidepressants do, suggesting a low ability of duloxetine to enter the brain. Alternatively, low drug concentrations may be interpreted in a sense of a missing residence time in cerebrospinal fluid due to active transport mechanisms out of this environment either back into the bloodstream or into the brain.

Associations between five-factor model of the Positive and Negative Syndrome Scale and plasma levels of monoamine metabolite in patients with schizophrenia

The five-factor model of the Positive and Negative Syndrome Scale (PANSS) for schizophrenia symptoms is the most common multiple-factor model used in analyses; its use may improve evaluation of symptoms in schizophrenia patients. Plasma monoamine metabolite levels are possible indicators of clinical symptoms or response to antipsychotics in schizophrenia. We investigated the association between five-factor model components and plasma monoamine metabolites levels to explore the model's biological basis. Plasma levels of homovanillic acid (HVA), 3-methoxy-4-hydroxyphenylglycol (MHPG), and 5-hydroxyindoleacetic acid (5-HIAA) were measured using high-performance liquid chromatography in 65 Japanese patients with schizophrenia. Significant negative correlation between plasma 5-HIAA levels and the depression/anxiety component was found. Furthermore, significant positive correlation was found between plasma MHPG levels and the excitement component. Plasma HVA levels were not correlated with any five-factor model component. These results suggest that the five-factor model of the PANSS may have a biological basis, and may be useful for elucidating the psychopathology of schizophrenia. Assessment using the five-factor model may enable understanding of monoaminergic dysfunction, possibly allowing more appropriate medication selection. Further studies of a larger number of first-episode schizophrenia patients are needed to confirm and extend these results.

Agomelatine Protection in an LPS-Induced Psychosis-Relevant Behavior Model

BACKGROUND The aim of this study was to investigate the effect of agomelatine in a psychosis-relevant behavior model. MATERIAL AND METHODS We used 18 adult male Wistar rats in this study. Twelve rats given LPS for endotoxemia were randomly divided into 2 groups (n=6). Group I was treated with 1 mL/kg 0.9% NaCl i.p. and Group II was treated with 40 mg/kg agomelatine. Six normal rats served as the control group and were not given LPS for endotoxemia. Cylindrical steel cages containing vertical and horizontal metal bars with top cover were used. Rats were put in these cages for the purpose of orientation for 10 min. Apomorphine was given to rats removed from cages, and then they were immediately put back in the cages for the purpose of observing stereotyped conduct. Brain HVA levels and plasma TNF-a levels were evaluated in tissue homogenates using ELISA. The proportion of malondialdehyde (MDA) was measured in samples taken from plasma for detection of lipid peroxidation similar to thiobarbituric acid reactive substances. RESULTS LPS induced-plasma TNF-α, brain TNF-α, and plasma MDA levels were significantly lower in the LPS+agomelatine group compared to the LPS+saline group (p<0.05). HVA levels and stereotype scores were significantly lower in the LPS+agomelatine group compared to the LPS+saline group (p <0.001). CONCLUSIONS Agomelatine reduced TNF-α, HVA, MDA levels, and the stereotype score in relevant models of psychosis. Our results suggest that the anti-inflammatory effect of agomelatine involved oxidant cleansing properties and that its effects on the metabolism of dopamine can play an important role in the model of psychosis.

Cerebrospinal fluid monoamine metabolite concentrations as intermediate phenotypes between glutamate-related genes and psychosis

Glutamate-related genes have been associated with schizophrenia, but the results have been ambiguous and difficult to replicate. Homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) are the major degradation products of the monoamines dopamine, serotonin and noradrenaline, respectively, and their concentrations in the cerebrospinal fluid (CSF), mainly HVA, have been associated with schizophrenia. In the present study, we hypothesized that CSF HVA, 5-HIAA and MHPG concentrations represent intermediate phenotypes in the association between glutamate-related genes and psychosis. To test this hypothesis, we searched for association between 238 single nucleotide polymorphisms (SNPs) in ten genes shown to be directly or indirectly implicated in glutamate transmission and CSF HVA, 5-HIAA and MHPG concentrations in 74 patients with psychotic disease. Thirty-eight nominally significant associations were found. Further analyses in 111 healthy controls showed that 87% of the nominal associations were restricted to the patients with psychosis. Some of the psychosis-only-associated SNPs found in the d-amino acid oxidase activator (DAOA) and the kynurenine 3-monooxygenase (KMO) genes have previously been reported to be associated with schizophrenia. The present results suggest that CSF monoamine metabolite concentrations may represent intermediate phenotypes in the association between glutamate-related genes and psychosis.

Current advances in biosampling for therapeutic drug monitoring of psychiatric CNS drugs

Many CNS drugs are effective for the treatment of psychiatric disorders. Psychotropic drugs work differently, thus clinical outcomes for many patients may be insufficient. For this reason it could be useful the measurement of drug levels for clinical decision-making. Analytical goals in therapeutic drug monitoring (TDM) should be established by selecting the appropriate biological matrix. The aim of this review is to highlight the usefulness of TDM for antiepileptics, antidepressants and antipsychotics, with a focus on current advances in biosampling. The literature on TDM was reviewed up to March 2015. An overview on the use of alternative biological matrices is provided to address the current issues and advances in the field of biosampling for psychiatric CNS drug TDM.

Distribution pattern of mirtazapine and normirtazapine in blood and CSF

RATIONALE

The aim of this study was to investigate the distribution pattern of mirtazapine and its metabolite normirtazapine (N-desmethylmirtazapine) in blood and cerebrospinal fluid (CSF).

OBJECTIVES AND METHODS

Concentrations of mirtazapine were measured in blood serum and CSF of 16 patients treated with daily doses of 7.5-60 mg. Daily doses were correlated with serum and CSF concentrations as well as serum levels with those in CSF.

RESULTS

Serum levels of mirtazapine and normirtazapine showed a strong relation to the daily dose of mirtazapine of r = +0.631 and r = +0.732, respectively (p < 0.01). Between the daily doses and the CSF levels of both mirtazapine and normirtazapine, we only found a trend-wise correlation (r = +0.535, p = 0.060). The correlation between mirtazapine and normirtazapine in serum and CSF was highly significant (r = +0.664, p = 0.005 and r = +0.885, p < 0.001, respectively). High discrepancies between (total) mirtazapine levels in serum and CSF indicate a low penetration into CSF with regard to the total serum concentration as the mean of the calculated penetration ratio was 0.16 (SD = 0.11). By correcting the penetration ratio for the plasma protein binding, the mean CSF/serum ratio for the unbound fraction was 1.05 (SD 0.72, range 0.56-3.19) indicating a high passage into CSF.

CONCLUSIONS

Findings indicate a good ability of mirtazapine and normirtazapine to overcome the blood-cerebrospinal fluid barrier and suggest a high ability to enter the brain with sufficient drug levels at the target sites within the brain contributing to clinical efficacy.

Polymorphisms in genes implicated in dopamine, serotonin and noradrenalin metabolism suggest association with cerebrospinal fluid monoamine metabolite concentrations in psychosis

BACKGROUND

Homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) are the major monoamine metabolites in the central nervous system (CNS). Their cerebrospinal fluid (CSF) concentrations, reflecting the monoamine turnover rates in CNS, are partially under genetic influence and have been associated with schizophrenia. We have hypothesized that CSF monoamine metabolite concentrations represent intermediate steps between single nucleotide polymorphisms (SNPs) in genes implicated in monoaminergic pathways and psychosis.

METHODS

We have searched for association between 119 SNPs in genes implicated in monoaminergic pathways [tryptophan hydroxylase 1 (TPH1), TPH2, tyrosine hydroxylase (TH), DOPA decarboxylase (DDC), dopamine beta-hydroxylase (DBH), catechol-O-methyltransferase (COMT), monoamine oxidase A (MAOA) and MAOB] and monoamine metabolite concentrations in CSF in 74 patients with psychotic disorder.

RESULTS

There were 42 nominally significant associations between SNPs and CSF monoamine metabolite concentrations, which exceeded the expected number (20) of nominal associations given the total number of tests performed. The strongest association (p = 0.0004) was found between MAOB rs5905512, a SNP previously reported to be associated with schizophrenia in men, and MHPG concentrations in men with psychotic disorder. Further analyses in 111 healthy individuals revealed that 41 of the 42 nominal associations were restricted to patients with psychosis and were absent in healthy controls.

CONCLUSIONS

The present study suggests that altered monoamine turnover rates in CNS reflect intermediate steps in the associations between SNPs and psychosis.

Use of translational pharmacodynamic biomarkers in early-phase clinical studies for schizophrenia

Schizophrenia is a severe mental disorder characterized by cognitive deficits, and positive and negative symptoms. The development of effective pharmacological compounds for the treatment of schizophrenia has proven challenging and costly, with many compounds failing during clinical trials. Many failures occur due to disease heterogeneity and lack of predictive preclinical models and biomarkers that readily translate to humans during early characterization of novel antipsychotic compounds. Traditional early-phase trials consist of single- or multiple-dose designs aimed at determining the safety and tolerability of an investigational compound in healthy volunteers. However, by incorporating a translational approach employing methodologies derived from preclinical studies, such as EEG measures and imaging, into the traditional Phase I program, critical information regarding a compound's dose-response effects on pharmacodynamic biomarkers can be acquired. Furthermore, combined with the use of patients with stable schizophrenia in early-phase clinical trials, significant 'de-risking' and more confident 'go/no-go' decisions are possible.

A neurobiological hypothesis of treatment-resistant depression - mechanisms for selective serotonin reuptake inhibitor non-efficacy

First-line treatment of major depression includes administration of a selective serotonin reuptake inhibitor (SSRI), yet studies suggest that remission rates following two trials of an SSRI are <50%. The authors examine the putative biological substrates underlying "treatment resistant depression (TRD)" with the goal of elucidating novel rationales to treat TRD. We look at relevant articles from the preclinical and clinical literature combined with clinical exposure to TRD patients. A major focus was to outline pathophysiological mechanisms whereby the serotonin system becomes impervious to the desired enhancement of serotonin neurotransmission by SSRIs. A complementary focus was to dissect neurotransmitter systems, which serve to inhibit the dorsal raphe. We propose, based on a body of translational studies, TRD may not represent a simple serotonin deficit state but rather an excess of midbrain peri-raphe serotonin and subsequent deficit at key fronto-limbic projection sites, with ultimate compromise in serotonin-mediated neuroplasticity. Glutamate, serotonin, noradrenaline, and histamine are activated by stress and exert an inhibitory effect on serotonin outflow, in part by "flooding" 5-HT1A autoreceptors by serotonin itself. Certain factors putatively exacerbate this scenario - presence of the short arm of the serotonin transporter gene, early-life adversity and comorbid bipolar disorder - each of which has been associated with SSRI-treatment resistance. By utilizing an incremental approach, we provide a system for treating the TRD patient based on a strategy of rescuing serotonin neurotransmission from a state of SSRI-induced dorsal raphe stasis. This calls for "stacked" interventions, with an SSRI base, targeting, if necessary, the glutamatergic, serotonergic, noradrenergic, and histaminergic systems, thereby successively eliminating the inhibitory effects each are capable of exerting on serotonin neurons. Future studies are recommended to test this biologically based approach for treatment of TRD.

Norepinephrine transporter occupancy in the human brain after oral administration of quetiapine XR

Quetiapine, originally developed as an antipsychotic, demonstrates efficacy in clinical studies of schizophrenia, bipolar mania and depression, major depressive disorder and generalized anxiety disorder. This broad spectrum of efficacy was not predicted from the preclinical pharmacology of quetiapine. Binding studies in vitro show that quetiapine and its major active human metabolite, norquetiapine, have moderate to high affinity for dopamine D2 and serotonin 5-HT2A receptors, while norquetiapine alone has high affinity for the norepinephrine transporter (NET). This positron emission tomography (PET) study measured NET occupancy in human subjects treated with extended-release quetiapine (quetiapine XR) at doses relevant in the treatment of depression. PET measurements using the specific NET radioligand (S,S)-[(18)F]FMeNER-D2 were performed before and after quetiapine XR treatment at 150 and 300 mg/d for 6-8 d in nine healthy males (aged 21-33 yr). Regions of interest were defined for the thalamus, using the caudate as reference region. NET occupancy was calculated using a target:reference region ratio method. Plasma concentrations of quetiapine and norquetiapine were monitored during PET measurements. Following quetiapine XR treatment, the mean NET occupancy in the thalamus was 19 and 35%, respectively, at quetiapine XR doses of 150 and 300 mg/d. The estimated plasma concentration of norquetiapine corresponding to 50% NET occupancy was 161 ng/ml. This is the first demonstration of NET occupancy by an antipsychotic in the human brain. NET inhibition is accepted as a mechanism of antidepressant activity. NET occupancy may therefore contribute to the broad spectrum of efficacy of quetiapine.

Plasma quetiapine in relation to prescribed dose and other factors: data from a therapeutic drug monitoring service, 2000-2011

OBJECTIVE

Suggested predose plasma quetiapine target ranges for effective therapy in schizophrenia lie between 50 and 500 µg/l. We aimed to examine data from a quetiapine therapeutic drug monitoring (TDM) service to assess the plasma quetiapine concentrations attained at specified doses in clinical practice.

METHOD

We studied TDM data from patients given immediate-release quetiapine in the period 2000-2011.

RESULTS

There were 946 samples from 487 patients (257 males, age at time of first sample, median [range] 34 [14-87] years, and 230 females, age at time of first sample, median [range] 38 [10-92] years). The plasma quetiapine concentration was <50 and <100 µg/l in 30% and 50% of samples, respectively (no quetiapine detected in 9% of samples). The relationship between dose and plasma quetiapine was poor. The mean (95% confidence interval [CI]) quetiapine dose was higher (t = 3.6, df = 446, p <0.01) in males versus females (641 [600-1240] and 548 [600-943] mg/day, respectively), although there was no difference in median dose (600 mg/day) or in the mean (95% CI) plasma quetiapine concentrations attained. Smoking habit had no discernible effect on plasma quetiapine concentration.

CONCLUSIONS

There was a poor relationship between dose and plasma quetiapine concentration in this study, as found by others. This is probably because of the short plasma half-life of the drug, at least in part. Nevertheless, quetiapine TDM can help assess adherence and measurement of quetiapine metabolites, notably N-desalkylquetiapine, as well as quetiapine itself may enhance the value of quetiapine TDM in future.

Cognitive efficacy of quetiapine in early-onset first-episode psychosis: a 12-week open label trial

Twenty-three adolescents with psychotic disorders, aged from 13 to 18 years, participated in a 12-week open label trial (17 adolescents completed the study) in order to examine the impact of quetiapine on clinical status and cognitive functions (encompassing processing speed, attention, short-term memory, long-term memory and executive function). An improvement in Clinical Global Impression and Positive and Negative Symptom Scale (P's ≤ 0.001) was observed. In addition, after controlling for amelioration of symptoms, a significant improvement was observed on one executive function (P = 0.044; Trail Making Part B). The remaining cognitive abilities showed stability. In addition, we observed an interaction between quetiapine doses (>300 mg/day or <300 mg/day) and time, where lower doses showed more improvement in verbal short-term memory (P = 0.048), inhibition abilities (P = 0.038) and positive symptoms (P = 0.020). The neuropsychological functioning of adolescents with psychotic disorders remained mainly stable after 12 weeks of treatment with quetiapine. However, lower doses seemed to have a better impact on two components of cognition (inhibition abilities and verbal short-term memory) and on positive symptoms.

D-amino acid oxidase activator gene (DAOA) variation affects cerebrospinal fluid homovanillic acid concentrations in healthy Caucasians

The D-amino acid oxidase activator (DAOA) protein regulates the function of D-amino oxidase (DAO), an enzyme that catalyzes the oxidative deamination of D-3,4-dihydroxyphenylalanine (D-DOPA) and D-serine. D-DOPA is converted to L-3,4-DOPA, a precursor of dopamine, whereas D-serine participates in glutamatergic transmission. We hypothesized that DAOA polymorphisms are associated with dopamine, serotonin and noradrenaline turnover in the human brain. Four single-nucleotide polymorphisms, previously reported to be associated with schizophrenia, were genotyped. Cerebrospinal fluid (CSF) samples were drawn by lumbar puncture, and the concentrations of the major dopamine metabolite homovanillic acid (HVA), the major serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) and the major noradrenaline metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) were measured. Two of the investigated polymorphisms, rs3918342 and rs1421292, were significantly associated with CSF HVA concentrations. Rs3918342 was found to be nominally associated with CSF 5-HIAA concentrations. None of the polymorphisms were significantly associated with MHPG concentrations. Our results indicate that DAOA gene variation affects dopamine turnover in healthy individuals, suggesting that disturbed dopamine turnover is a possible mechanism behind the observed associations between genetic variation in DAOA and behavioral phenotypes in humans.