In vivo imaging of serotonin transporter occupancy by means of SPECT and [123I]ADAM in healthy subjects administered different doses of escitalopram or citalopram

Update Lessons from PET Imaging Part II: A Systematic Critical Review on Therapeutic Plasma Concentrations of Antidepressants

BACKGROUND

Compared with antipsychotics, the relationship between antidepressant blood (plasma or serum) concentrations and target engagement is less well-established.

METHODS

We have discussed the literature on the relationship between plasma concentrations of antidepressant drugs and their target occupancy. Antidepressants reviewed in this work are citalopram, escitalopram, fluoxetine, fluvoxamine, paroxetine, sertraline, venlafaxine, duloxetine, milnacipran, tricyclic antidepressants (amitriptyline, nortriptyline, and clomipramine), bupropion, tranylcypromine, moclobemide, and vortioxetine. Four electronic databases were systematically searched.

RESULTS

We included 32 articles published 1996-2022. A strong relationship between serotonin transporter (SERT) occupancy and drug concentration is well established for selective serotonin reuptake inhibitors. Lower limits of recommended therapeutic reference ranges largely corroborate with the findings from positron emission tomography studies (80% SERT occupancy). Only a few novel studies have investigated alternative targets, that is, norepinephrine transporters (NETs), dopamine transporters (DATs), or monoamine oxidase A (MAO-A). For certain classes of drugs, positron emission tomography study data are inconclusive. Low DAT occupancy after bupropion treatment speculates its discussed mechanism of action. For MAO inhibitors, a correlation between drug concentration and MAO-A occupancy could not be established.

CONCLUSIONS

Neuroimaging studies are critical in TDM-guided therapy for certain antidepressants, whereas for bupropion and MAO inhibitors, the available evidence offers no further insight. Evidence for selective serotonin reuptake inhibitors is strong and justifies a titration toward suggested ranges. For SNRIs, duloxetine, and venlafaxine, NETs are sufficiently occupied, well above the SERT efficacy threshold. For these drugs, a titration toward higher concentrations (within the recommended range) should be considered in case of no response at lower concentrations.

Vortioxetine as a potential alternative for patients with escitalopram-induced jitteriness/anxiety syndrome: A report of three cases

Background

Jitteriness/anxiety syndrome is a recognized adverse effect observed during the initiation or change of dose in antidepressant treatment. Managing patients who develop this syndrome remains a challenge. While escitalopram is a widely used antidepressant known to cause these symptoms, this report explores vortioxetine as a therapeutic alternative.

Case Presentation

Three distinct clinical scenarios were observed in patients who manifested jitteriness/anxiety syndrome while on escitalopram treatment for depression. Patient A was initiated on escitalopram and experienced an initial alleviation in depressive symptoms, but 3 months later displayed mood elevation, talkativeness, and increased activity, which disturbed his daily life. A transition to vortioxetine subsequently resolved the mood elevation. Patient B exhibited elevated mood, hyperactivity, irritability, and talkativeness just 6 days post-initiation of treatment with escitalopram. After the discontinuation of escitalopram and unsuccessful trials with aripiprazole, lurasidone, and lamotrigine, her depressive mood intensified, culminating in suicidal ideation. Starting vortioxetine led to a consistent improvement of her symptoms, and she resumed work and was emotionally stable. Patient C was initially diagnosed with bipolar disorder and faced a relapse into depression despite undergoing various treatments. After 2 weeks on escitalopram, she exhibited irritability and self-harm urges. Three months later, after being re-diagnosed with depressive disorders with anxious distress, vortioxetine was administered, which significantly reduced her depressive symptoms and allowed her to continue her education.

Conclusion

Vortioxetine presents as a promising therapeutic alternative that is worth considering for patients with escitalopram-induced jitteriness/anxiety syndrome.

Modulation of functional networks related to the serotonin neurotransmitter system by citalopram: Evidence from a multimodal neuroimaging study

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) potentiate serotonergic neurotransmission by blocking the serotonin transporter (5-HTT), but the functional brain response to SSRIs involves neural circuits beyond regions with high 5-HTT expression. Currently, it is unclear whether and how changes in 5-HTT availability after SSRI administration modulate brain function of key serotoninergic circuits, including those characterized by high availability of the serotonin 1A receptor (5-HT1AR).

AIM

We investigated the association between 5-HTT availability and 5-HTT- and 5-HT1AR-enriched functional connectivity (FC) after an acute citalopram challenge.

METHODS

We analyzed multimodal data from a dose-response, placebo-controlled, double-blind study, in which 45 healthy women were randomized into three groups receiving placebo, a low (4 mg), or high (16 mg) oral dose of citalopram. Receptor-Enhanced Analysis of functional Connectivity by Targets was used to estimate 5-HTT- and 5-HT1AR-enriched FC from resting-state and task-based fMRI. 5-HTT availability was determined using [123I]FP-CIT single-photon emission computerized tomography.

RESULTS

5-HTT availability was negatively correlated with resting-state 5-HTT-enriched FC, and with task-dependent 5-HT1AR-enriched FC. Our exploratory analyses revealed lower 5-HT1AR-enriched FC in the low-dose group compared to the high-dose group at rest and the placebo group during the emotional face-matching task.

CONCLUSIONS

Taken together, our findings provide evidence for differential links between 5-HTT availability and brain function within 5-HTT and 5-HT1AR pathways and in context- and dose-dependent manner. As such, they support a potential pivotal role of the 5-HT1AR in the effects of citalopram on the brain and add to its potential as a therapeutic avenue for mood and anxiety disturbances.

The attention-emotion interaction in healthy female participants on oral contraceptives during 1-week escitalopram intake

Previous findings in healthy humans suggest that selective serotonin reuptake inhibitors (SSRIs) modulate emotional processing via earlier changes in attention. However, many previous studies have provided inconsistent findings. One possible reason for such inconsistencies is that these studies did not control for the influence of either sex or sex hormone fluctuations. To address this inconsistency, we administered 20 mg escitalopram or placebo for seven consecutive days in a randomized, double-blind, placebo-controlled design to sixty healthy female participants with a minimum of 3 months oral contraceptive (OC) intake. Participants performed a modified version of an emotional flanker task before drug administration, after a single dose, after 1 week of SSRI intake, and after a 1-month wash-out period. Supported by Bayesian analyses, our results do not suggest a modulatory effect of escitalopram on behavioral measures of early attentional-emotional interaction in female individuals with regular OC use. While the specific conditions of our task may be a contributing factor, it is also possible that a practice effect in a healthy sample may mask the effects of escitalopram on the attentional-emotional interplay. Consequently, 1 week of escitalopram administration may not modulate attention toward negative emotional distractors outside the focus of attention in healthy female participants taking OCs. While further research in naturally cycling females and patient samples is needed, our results represent a valuable contribution toward the preclinical investigation of antidepressant treatment.

Systematic review and meta-analysis on the therapeutic reference range for escitalopram: Blood concentrations, clinical effects and serotonin transporter occupancy

INTRODUCTION

A titration within a certain therapeutic reference range presupposes a relationship between the blood concentration and the therapeutic effect of a drug. However, this has not been systematically investigated for escitalopram. Furthermore, the recommended reference range disagrees with mean steady state concentrations (11-21 ng/ml) that are expected under the approved dose range (10-20 mg/day). This work systematically investigated the relationships between escitalopram dose, blood levels, clinical effects, and serotonin transporter occupancy.

METHODS

Following our previously published methodology, relevant articles were systematically searched and reviewed for escitalopram.

RESULTS

Of 1,032 articles screened, a total of 30 studies met the eligibility criteria. The included studies investigated escitalopram blood levels in relationship to clinical effects (9 studies) or moderating factors on escitalopram metabolism (12 studies) or serotonin transporter occupancy (9 studies). Overall, the evidence for an escitalopram concentration/effect relationship is low (level C).

CONCLUSION

Based on our findings, we propose a target range of 20-40 ng/ml for antidepressant efficacy of escitalopram. In maintenance treatment, therapeutic response is expected, when titrating patients above the lower limit. The lower concentration threshold is strongly supported by findings from neuroimaging studies. The upper limit for escitalopram's reference range rather reflects a therapeutic maximum than a tolerability threshold, since the incidence of side effects in general is low. Concentrations above 40 ng/ml should not necessarily result in dose reductions in case of good clinical efficacy and tolerability. Dose-related escitalopram concentrations in different trials were more than twice the expected concentrations from guideline reports.

SYSTEMATIC REVIEW REGISTRATION

[https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=215873], identifier [CRD42020215873].

The relationship between dose and serotonin transporter occupancy of antidepressants-a systematic review

Brain imaging techniques enable the visualization of serotonin transporter (SERT) occupancy as a measure of the proportion of SERT blocked by an antidepressant at a given dose. We aimed to systematically review the evidence on the relationship between antidepressant dose and SERT occupancy. We searched PubMed and Embase (last search 20 May 2021) for human in vivo, within-subject PET, or SPECT studies measuring SERT occupancy at any dose of any antidepressant with highly selective radioligands ([¹¹C]-DASB, [¹²³I]-ADAM, and [¹¹C]-MADAM). We summarized and visualized the dose-occupancy relationship for antidepressants across studies, overlaying the plots with a curve based on predicted values of a standard 2-parameter Michaelis-Menten model fitted using the observed data. We included seventeen studies of 10 different SSRIs, SNRIs, and serotonin modulators comprising a total of 294 participants, involving 309 unique occupancy measures. Overall, following the Michaelis-Menten equation, SERT occupancy increased with a higher dose in a hyperbolic relationship, with occupancy increasing rapidly at lower doses and reaching a plateau at approximately 80% at the usual minimum recommended dose. All the studies were small, only a few investigated the same antidepressant, dose, and brain region, and few reported information on factors that may influence SERT occupancy. The hyperbolic dose-occupancy relationship may provide mechanistic insight of relevance to the limited clinical benefit of dose-escalation in antidepressant treatment and the potential emergence of withdrawal symptoms. The evidence is limited by non-transparent reporting, lack of standardized methods, small sample sizes, and short treatment duration. Future studies should standardize the imaging and reporting procedures, measure occupancy at lower antidepressant doses, and investigate the moderators of the dose-occupancy relationship.

Tools for optimising pharmacotherapy in psychiatry (therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests): focus on antidepressants

Objectives: More than 40 drugs are available to treat affective disorders. Individual selection of the optimal drug and dose is required to attain the highest possible efficacy and acceptable tolerability for every patient.Methods: This review, which includes more than 500 articles selected by 30 experts, combines relevant knowledge on studies investigating the pharmacokinetics, pharmacodynamics and pharmacogenetics of 33 antidepressant drugs and of 4 drugs approved for augmentation in cases of insufficient response to antidepressant monotherapy. Such studies typically measure drug concentrations in blood (i.e. therapeutic drug monitoring) and genotype relevant genetic polymorphisms of enzymes, transporters or receptors involved in drug metabolism or mechanism of action. Imaging studies, primarily positron emission tomography that relates drug concentrations in blood and radioligand binding, are considered to quantify target structure occupancy by the antidepressant drugs in vivo. Results: Evidence is given that in vivo imaging, therapeutic drug monitoring and genotyping and/or phenotyping of drug metabolising enzymes should be an integral part in the development of any new antidepressant drug.Conclusions: To guide antidepressant drug therapy in everyday practice, there are multiple indications such as uncertain adherence, polypharmacy, nonresponse and/or adverse reactions under therapeutically recommended doses, where therapeutic drug monitoring and cytochrome P450 genotyping and/or phenotyping should be applied as valid tools of precision medicine.

Modulation of premotor cortex response to sequence motor learning during escitalopram intake

The contribution of selective serotonin reuptake inhibitors to motor learning by inducing motor cortical plasticity remains controversial given diverse findings from positive preclinical data to negative findings in recent clinical trials. To empirically address this translational disparity, we use functional magnetic resonance imaging in a double-blind, randomized controlled study to assess whether 20 mg escitalopram improves sequence-specific motor performance and modulates cortical motor response in 64 healthy female participants. We found decreased left premotor cortex responses during sequence-specific learning performance comparing single dose and steady escitalopram state. Escitalopram plasma levels negatively correlated with the premotor cortex response. We did not find evidence in support of improved motor performance after a week of escitalopram intake. These findings do not support the conclusion that one week escitalopram intake increases motor performance but could reflect early adaptive plasticity with improved neural processing underlying similar task performance when steady peripheral escitalopram levels are reached.

A single dose of escitalopram blunts the neural response in the thalamus and caudate during monetary loss

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) show acute effects on the neural processes associated with negative affective bias in healthy people and people with depression. However, whether and how SSRIs also affect reward and punishment processing on a similarly rapid time scale remains unclear.

METHODS

We investigated the effects of an acute and clinically relevant dose (20 mg) of the SSRI escitalopram on brain response during reward and punishment processing in 19 healthy participants. In a doubleblind, placebo-controlled study using functional MRI, participants performed a well-established monetary reward task at 3 time points: at baseline; after receiving placebo or escitalopram; and after receiving placebo or escitalopram following an 8-week washout period.

RESULTS

Acute escitalopram administration reduced blood-oxygen-level-dependent (BOLD) response during punishment feedback in the right thalamus (family-wise error corrected [FWE] p = 0.013 at peak level) and the right caudate head (pFWE = 0.011 at peak level) compared to placebo. We did not detect any significant BOLD changes during reward feedback.

LIMITATIONS

We included only healthy participants, so interpretation of findings are limited to the healthy human brain and require future testing in patient populations. The paradigm we used was based on monetary stimuli, and results may not be generalizable to other forms of reward.

CONCLUSION

Our findings extend theories of rapid SSRI action on the neural processing of rewarding and aversive stimuli and suggest a specific and acute effect of escitalopram in the punishment neurocircuitry.

Attenuation of auditory mismatch negativity in serotonin transporter knockout mice with anxiety-related behaviors

As the first-line antidepressant drugs, selective serotonin reuptake inhibitors (SSRIs) have efficacy in controlling the symptoms of depression. However, adverse events such as anxiety and hearing disorders were usually observed in patients and even healthy volunteers during the initial phase of SSRI administration. Hearing disorders, including auditory hallucination and tinnitus, are not only highly comorbid with mental disorders but also acknowledged factors that induce psychiatric disorders. The pharmacological and neural mechanisms underlying SSRI-induced anxiety and hearing disorders are not clear. In particularly, the methods evaluating hearing disorders are not well established in animal models, limiting the pre-clinical research on its mechanism. In the present study, we examined the mismatch negativity (MMN), a cognitive component of auditory event-related potential (ERP), to evaluate the hearing process of auditory cortex in mice. Under the acute administration of citalopram, a widely used SSRI, the anxiety-related behaviors and reduced MMN were observed in mice. Serotonin transporter (SERT) is a potential target of SSRIs. The anxiety-related behaviors and reduced MMN were also observed in SERT knockout mice, implying the role of SERT in anxiety and hearing disorders induced by SSRIs. Meanwhile, the auditory brainstem response and initial components of auditory ERP were kept intact in SERT knockout mice, suggesting that hearing neural pathway is less affected by serotonergic system. Our study suggests that the SERT deficient mice might represent a useful animal model in the investigation of the anxiety and hearing disorders during the SSRI treatment.

Innovative Molecular Imaging for Clinical Research, Therapeutic Stratification, and Nosography in Neuroscience

Over the past few decades, several radiotracers have been developed for neuroimaging applications, especially in PET. Because of their low steric hindrance, PET radionuclides can be used to label molecules that are small enough to cross the blood brain barrier, without modifying their biological properties. As the use of 11C is limited by its short physical half-life (20 min), there has been an increasing focus on developing tracers labeled with 18F for clinical use. The first such tracers allowed cerebral blood flow and glucose metabolism to be measured, and the development of molecular imaging has since enabled to focus more closely on specific targets such as receptors, neurotransmitter transporters, and other proteins. Hence, PET and SPECT biomarkers have become indispensable for innovative clinical research. Currently, the treatment options for a number of pathologies, notably neurodegenerative diseases, remain only supportive and symptomatic. Treatments that slow down or reverse disease progression are therefore the subject of numerous studies, in which molecular imaging is proving to be a powerful tool. PET and SPECT biomarkers already make it possible to diagnose several neurological diseases in vivo and at preclinical stages, yielding topographic, and quantitative data about the target. As a result, they can be used for assessing patients' eligibility for new treatments, or for treatment follow-up. The aim of the present review was to map major innovative radiotracers used in neuroscience, and explain their contribution to clinical research. We categorized them according to their target: dopaminergic, cholinergic or serotoninergic systems, β-amyloid plaques, tau protein, neuroinflammation, glutamate or GABA receptors, or α-synuclein. Most neurological disorders, and indeed mental disorders, involve the dysfunction of one or more of these targets. Combinations of molecular imaging biomarkers can afford us a better understanding of the mechanisms underlying disease development over time, and contribute to early detection/screening, diagnosis, therapy delivery/monitoring, and treatment follow-up in both research and clinical settings.

Dose-dependent effects of the selective serotonin reuptake inhibitor citalopram: A combined SPECT and phMRI study

BACKGROUND

Serotonin transporter blockers, like citalopram, dose-dependently bind to the serotonin transporter. Pharmacological magnetic resonance imaging (phMRI) can be used to non-invasively monitor effects of serotonergic medication. Although previous studies showed that phMRI can measure the effect of a single dose of serotoninergic medication, it is currently unclear whether it can also detect dose-dependent effects.

AIMS

To investigate the dose-dependent phMRI response to citalopram and compared this with serotonin transporter occupancy, measured with single photon emission computed tomography (SPECT).

METHODS

Forty-five healthy females were randomized to pre-treatment with placebo, a low (4 mg) or clinically standard (16 mg) oral citalopram dose. Prior to citalopram, and 3 h after, subjects underwent SPECT scanning. Subsequently, a phMRI scan with a citalopram challenge (7.5 mg intravenously) was conducted. Change in cerebral blood flow in response to the citalopram challenge was assessed in the thalamus and occipital cortex (control region).

RESULTS

Citalopram dose-dependently affected serotonin transporter occupancy, as measured with SPECT. In addition, citalopram dose-dependently affected the phMRI response to intravenous citalopram in the thalamus (but not occipital cortex), but phMRI was less sensitive in distinguishing between groups than SPECT. Serotonin transporter occupancy showed a trend-significant correlation to thalamic cerebral blood flow change.

CONCLUSION

These results suggest that phMRI likely suffers from higher variation than SPECT, but that these techniques probably also assess different functional aspects of the serotonergic synapse; therefore phMRI could complement positron emission tomography/SPECT for measuring effects of serotonergic medication.

Serotonin transporter occupancy by the SSRI citalopram predicts default-mode network connectivity

The default mode network (DMN) is an important connectivity hub, and alterations may play a role in the pathophysiology of several neuropsychiatric disorders. Despite the growing body of research on DMN (dys)function, the underlying neurochemical substrate remains to be elucidated. The serotonergic neurotransmitter system has been suggested to play a substantial role in modulating the DMN. Therefore, we investigated the association between serotonin transporter (SERT) occupancy by the selective serotonin reuptake inhibitor citalopram and DMN functional connectivity. Forty-five healthy female volunteers (mean age = 21.6y) participated in a double-dose study. The subjects were randomized to pre-treatment with placebo, a low (4 mg; 'low group') or clinically standard (16 mg; 'high group') oral citalopram dose (corresponding to 0%, ∼40% and ∼80% SERT occupancy, respectively). They underwent [¹²³I]FP-CIT single-photon emission computed tomography (SPECT) imaging to assess SERT occupancy. In addition, resting-state functional magnetic resonance imaging was used to measure DMN connectivity. With non-parametric permutation testing we assessed the association between SERT occupancy and DMN connectivity. We found that SERT occupancy by citalopram was negatively associated with DMN connectivity with a number of cortical regions, including the anterior cingulate cortex (ACC), paracingulate gyrus, postcentral gyrus, superior parietal gyrus and temporal pole. These findings provide further neurochemical evidence that the serotonin system dose-dependently modulates DMN function.

The allosteric citalopram binding site differentially interferes with neuronal firing rate and SERT trafficking in serotonergic neurons

Citalopram is a clinically applied selective serotonin re-uptake inhibitor for antidepressant pharmacotherapy. It consists of two enantiomers, S-citalopram (escitalopram) and R-citalopram, of which escitalopram exerts the antidepressant therapeutic effect and has been shown to be one of the most efficient antidepressants, while R-citalopram antagonizes escitalopram via an unknown molecular mechanism that may depend on binding to a low-affinity allosteric binding site of the serotonin transporter. However, the precise mechanism of antidepressant regulation of the serotonin transporter by citalopram enantiomers still remains elusive. Here we investigate escitalopram׳s acute effect on (1) serotonergic neuronal firing in transgenic mice that express the human serotonin transporter without and with a mutation that disables the allosteric binding site, and (2) regulation of the serotonin transporter׳s cell surface localization in stem cell-derived serotonergic neurons. Our results demonstrate that escitalopram inhibited neuronal firing less potently in the mouse line featuring a mutation that abolishes the function of the allosteric binding site and induced serotonin transporter internalization independently of the allosteric binding site mechanism. Furthermore, citalopram enantiomers dose-dependently induced serotonin transporter internalization. In conclusion, this study provides new insight into antidepressant effects exerted by citalopram enantiomers in presence and absence of a functional allosteric binding site.

Impact of 5-HTTLPR on SSRI serotonin transporter blockade during emotion regulation: A preliminary fMRI study

BACKGROUND

The short ('S') allele of the serotonin transporter (5-HTT)-linked polymorphic region (5-HTTLPR) is associated with increased negative emotion processing bias, and this polymorphism moderates acute effects of selective serotonin reuptake inhibitor (SSRI) treatment. In this preliminary study, we explore the moderating effect of 5-HTTLPR on the impact of the SSRI, escitalopram during emotion regulation of negative emotional stimuli.

METHOD

Thirty-six healthy Caucasian, female participants underwent two fMRI scanning sessions following single dose escitalopram and placebo administration separated by a seven-day washout period according to a double-blind, randomized, placebo-controlled crossover design. Functional connectivity analysis was employed with a left (L) amygdala seed and a right interior frontal gyrus (R IFG) target.

RESULTS

Changes in functional connectivity with emotion regulation and treatment were linearly related to 5-HTTLPR 'L' allele load such that negative R IFG-L amygdala connectivity was increased with an increasing number of 'L' alleles. Therefore, escitalopram may facilitate the effects of reappraisal by enhancing negative functional connectivity, a finding that is greatest in participants homozygous for the 'L' allele and least in those homozygous for the 'S' allele.

LIMITATIONS

Sub-samples of the homozygote 'S/S' and 'L/L' 5-HTTLPR groupings were small. However, the within-subjects nature of the experiment and observing changes at the individual subject level increases our confidence in the findings of the present study.

CONCLUSIONS

The present study elucidates a potential neural mechanism by which antidepressant treatment produces differential treatment outcomes dependent on the 5-HTTLPR polymorphism, providing new and important leads for models of antidepressant action.

Serotonin reuptake inhibitors and serotonin transporter genotype modulate performance monitoring functions but not their electrophysiological correlates

Serotonin (5-HT) has been hypothesized to be implicated in performance monitoring by promoting behavioral inhibition in the face of aversive events. However, it is unclear whether this is restricted to external (punishment) or includes internal (response errors) events. The aim of the current study was to test whether higher 5-HT levels instigate inhibition specifically in the face of errors, measured as post-error slowing (PES), and whether this is represented in electrophysiological correlates of error processing, namely error-related negativity (ERN) and positivity. Therefore, from a large sample of human subjects (n = 878), two extreme groups were formed regarding hypothesized high and low 5-HT transporter (5-HTT) expression based on 5-HTTLPR and two additional single nucleotide polymorphisms (rs25531, rs25532). Seventeen higher (LL) and 15 lower (SS) expressing Caucasian subjects were administered the selective serotonin reuptake inhibitor (SSRI) citalopram (10 mg) intravenously in a double-blind crossover design. We found pharmacogenetic evidence for a role of 5-HT in mediating PES: SSRI administration increased PES in both genetic groups, and SS subjects displayed higher PES. These effects were absent on post-conflict slowing. However, ERN and error positivity were unaffected by pharmacogenetic factors, but ERN was decoupled from behavioral adaptation by SSRI administration in the LL group. Thus, pharmacogenetic evidence suggests that increased 5-HT levels lead to behavioral inhibition in the context of internal aversive events, but electrophysiological correlates of performance monitoring appear unrelated to the 5-HT system. Therefore, our findings are consistent with theories suggesting that 5-HT mediates the link between aversive processing and inhibition.

Serotonin transporter availability may moderate the association between perceiving stress and depressive tendencies - A SPECT with 5-HTTLPR genotyping study

It was found that serotonin transporter (SERT) gene (5-HTTLPR) polymorphism may moderate the association between perceiving stress and depressive tendency. Although SERT availability in the central nervous system could be associated with 5-HTTLPR polymorphism, whether SERT availability moderates the association between stress and depressive tendency is unclear. This study aimed to investigate whether there is a SERT availability×environmental stress interaction effect, as well as a gene-by-environmental (G×E) interaction effect, using single-photon emission computed tomography (SPECT) with a serotonin transporter radiotracer, [(123)I]ADAM. 87 healthy volunteers were enrolled. The SERT availability was approximated using SPECT with [(123)I]ADAM. Stress and depressive tendencies were measured by the Recent Life Change Questionnaire (RLCQ) and the Taiwanese Depression Questionnaire (TDQ), respectively. A significant interaction of sex×RLCQ×thalamic SERT availability on the TDQ was found, and this effect was robust after controlling for the effect of the SS genotype. The interaction of RLCQ×thalamic SERT availability on the TDQ was significant among males. In particular, a significant association between RLCQ and TDQ (Spearman correlation, ρ=0.64, p<0.01) was found among male subjects with a lower level of thalamic SERT availability. SERT availability may play a role in depressive tendency when under perceived stress among healthy individuals, independent of G×E. This finding provides new evidence that confirms the role of the serotonergic system in the association between stress and depression. Males with lower levels of SERT availability may be more vulnerable to the effects of negative life events.

Improving response inhibition systems in frontotemporal dementia with citalopram

Disinhibition is a cardinal feature of the behavioural variant of frontotemporal dementia, presenting as impulsive and impetuous behaviours that are often difficult to manage. The options for symptomatic treatments are limited, but a potential target for therapy is the restoration of serotonergic function, which is both deficient in behavioural variant frontotemporal dementia and closely associated with inhibitory control. Based on preclinical studies and psychopharmacological interventions in other disorders, we predicted that inhibition would be associated with the right inferior frontal gyrus and dependent on serotonin. Using magnetoencephalography and electroencephalography of a Go-NoGo paradigm, we investigated the neural basis of behavioural disinhibition in behavioural variant frontotemporal dementia and the effect of selective serotonin reuptake inhibition on the neural systems for response inhibition. In a randomized double-blinded placebo-controlled crossover design study, 12 patients received either a single 30 mg dose of citalopram or placebo. Twenty age-matched healthy controls underwent the same magnetoencephalography/electroencephalography protocol on one session without citalopram, providing normative data for this task. In the control group, successful NoGo trials evoked two established indices of successful response inhibition: the NoGo-N2 and NoGo-P3. Both of these components were significantly attenuated by behavioural variant frontotemporal dementia. Cortical sources associated with successful inhibition in control subjects were identified in the right inferior frontal gyrus and anterior temporal lobe, which have been strongly associated with behavioural inhibition in imaging and lesion studies. These sources were impaired by behavioural variant frontotemporal dementia. Critically, citalopram enhanced the NoGo-P3 signal in patients, relative to placebo treatment, and increased the evoked response in the right inferior frontal gyrus. Voxel-based morphometry confirmed significant atrophy of inferior frontal gyrus, alongside insular, orbitofrontal and temporal cortex in our patient cohort. Together, these data suggest that the dysfunctional prefrontal cortical systems underlying response inhibition deficits in behavioural variant frontotemporal dementia can be partially restored by increasing serotonergic neurotransmission. The results support a translational neuroscience approach to impulsive neurological disorders and indicate the potential for symptomatic treatment of behavioural variant frontotemporal dementia including serotonergic strategies to improve disinhibition.media-1vid110.1093/brain/awv133_video_abstractawv133_video_abstract.

Disproportionate Reduction of Serotonin Transporter May Predict the Response and Adherence to Antidepressants in Patients with Major Depressive Disorder: A Positron Emission Tomography Study with 4-[18F]-ADAM

BACKGROUND

Many lines of evidence suggest the role of serotonin transporter (SERT)-mediated reuptake of serotonin in the pathophysiology and treatment of major depressive disorder (MDD). This study aimed to examine whether the pretreatment of SERT binding potential or SERT binding ratio between terminal projection regions relative to the midbrain raphe nuclei was associated with treatment outcomes to SERT-targeted antidepressants.

METHODS

We recruited 39 antidepressant-naïve patients with MDD and 39 heathy controls. Positron emission tomography with N,N-dimethyl-2-(2-amino-4-[(18)F]fluorophenylthio)benzylamine (4-[(18)F]-ADAM) was used to measure in vivo SERT availability prior to antidepressant treatment. The 21-item Hamilton Depression Rating Scale (HDRS) was use to assess the severity of depression from baseline to week 6. All the patients with MDD had HDRS scores of 18 or more.

RESULTS

Pretreatment SERT binding in the thalamus and striatum positively correlated with an early reduction in HDRS scores at week 3. Nonresponders and dropout patients showed a proportionate reduction in SERT binding in the terminal projection regions and midbrain compared to healthy controls. In contrast, a disproportionate reduction in SERT binding in the terminal projection regions relative to midbrain was observed in responders.

CONCLUSIONS

The results of this study suggested that a disproportionate reduction in SERT binding between terminal projection regions and midbrain may predict better treatment outcomes in patients with MDD.

(S)-citalopram influences amygdala modulation in healthy subjects: a randomized placebo-controlled double-blind fMRI study using dynamic causal modeling

Citalopram and Escitalopram are gold standard pharmaceutical treatment options for affective, anxiety, and other psychiatric disorders. However, their neurophysiologic function on cortico-limbic circuits is incompletely characterized. Here we studied the neuropharmacological influence of Citalopram and Escitalopram on cortico-limbic regulatory processes by assessing the effective connectivity between orbitofrontal cortex (OFC) and amygdala using dynamic causal modeling (DCM) applied to functional MRI data. We investigated a cohort of 15 healthy subjects in a randomized, crossover, double-blind design after 10days of Escitalopram (10mg/d (S)-citalopram), Citalopram (10mg/d (S)-citalopram and 10mg/d (R)-citalopram), or placebo. Subjects performed an emotional face discrimination task, while undergoing functional magnetic resonance imaging (fMRI) scanning at 3 Tesla. As hypothesized, the OFC, in the context of the emotional face discrimination task, exhibited a down-regulatory effect on amygdala activation. This modulatory effect was significantly increased by (S)-citalopram, but not (R)-citalopram. For the first time, this study shows that (1) the differential effects of the two enantiomers (S)- and (R)-citalopram on cortico-limbic connections can be demonstrated by modeling effective connectivity methods, and (2) one of their mechanisms can be linked to an increased inhibition of amygdala activation by the orbitofrontal cortex.

The impact of 5-HTTLPR on acute serotonin transporter blockade by escitalopram on emotion processing: preliminary findings from a randomised, crossover fMRI study

OBJECTIVE

Benefit from antidepressant treatment such as selective serotonin reuptake inhibitors (SSRIs) may depend on individual differences in acute effects on neural emotion processing. The short ('S') allele of the serotonin transporter (5-HTT)-linked polymorphic region (5-HTTLPR) is associated with both negative emotion processing biases and poorer treatment outcomes. Therefore, the aim of the present study was to explore the effects of 5-HTTLPR on the impact of the SSRI escitalopram during processing of positive and negative emotional images, as well as neutral stimuli.

METHODS

The study employed a double-blind, randomised, placebo-controlled crossover design on 36 healthy Caucasian female participants who underwent functional magnetic resonance imaging (fMRI) scanning following placebo or escitalopram treatment, separated by a 7-day washout period.

RESULTS

Changes in the left amygdala signal with escitalopram treatment during processing of emotional stimuli were linearly related to the 5-HTTLPR 'S' allele load such that the signal to positive stimuli decreased and the signal to negative stimuli increased with an increasing number of low-expressing 'S' alleles. While 5-HTTLPR subgroups were small in size, individual subject changes with treatment and task condition increase confidence in the findings.

CONCLUSIONS

While preliminary, our findings comprise the first pharmacogenetic study demonstrating an effect of the 5-HTTLPR 'S' allele load on escitalopram-induced changes in amygdala activity during emotional processing, consistent with a 5-HTT expression dosage model. The present findings have implications for the impact of this polymorphism on antidepressant efficacy in patients with mood and anxiety disorders.

The interaction of escitalopram and R-citalopram at the human serotonin transporter investigated in the mouse

RATIONALE

Escitalopram appears to be a superior antidepressant to racemic citalopram. It has been hypothesized that binding of R-citalopram to the serotonin transporter (SERT) antagonizes escitalopram binding to and inhibition of the SERT, there by curtailing the elevation of extracellular 5-hydroxytryptamine (5-HTExt), and hence anti-depressant efficacy. Further, it has been suggested that a putative allosteric binding site is important for binding of escitalopram to the primary, orthosteric, site, and for R-citalopram's inhibition here of.

OBJECTIVES

Primary: Investigate at the human (h)SERT, at clinical relevant doses, whether R-citalopram antagonizes escitalopram-induced 5-HTExt elevation. Secondary: Investigate whether abolishing the putative allosteric site affects escitalopram-induced 5-HTExt elevation and/or modulates the effect of R-citalopram.

METHODS

Recombinant generation of hSERT transgenic mice; in vivo microdialysis; SERT binding; pharmacokinetics; 5-HT sensitive behaviors (tail suspension, marble burying).

RESULTS

We generated mice expressing either the wild-type human SERT (hSERT(WT)) or hSERT carrying amino acid substitutions (A505V, L506F, I507L, S574T and I575T) collectively abolishing the putative allosteric site (hSERT(ALI/VFL+SI/TT)). One mg/kg escitalopram yielded clinical relevant plasma levels and brain levels consistent with therapeutic SERT occupancy. The hSERT mice showed normal basal 5-HTExt levels. Escitalopram-induced 5-HTExt elevation was not decreased by R-citalopram co-treatment and was unaffected by loss of the allosteric site. The behavioral effects of the clinically relevant escitalopram dose were small and tended to be enhanced by R-citalopram co-administration.

CONCLUSIONS

We find no evidence that R-citalopram directly antagonizes escitalopram or that the putative allosteric site is important for hSERT inhibition by escitalopram.

Diabetes with comorbid depression: role of SSRI in better glycemic control

INTRODUCTION

The presence of depression in patients with diabetes mellitus is reported to be associated with poor glycemic control and an increased risk of diabetic complications. Treatment of depression with selective serotonin reuptake inhibitors (SSRIs) may improve glycemic control and may be beneficial for patients with comorbid depression and diabetes.

AIMS AND OBJECTIVE

To study the effect of Escitalopram (SSRI) in patients with diabetes mellitus with comorbid depression and the relationship of treatment response for depression and glycemic control.

RESEARCH DESIGN AND METHODS

40 patients received open-label Escitalopram therapy for up to 12 weeks. Clinical outcome measures included Hamilton Depression rating scale (HAM-D) assessment at 3, 6, and 12 weeks. In addition, fasting and post-prandial plasma glucose level, weight and waist circumference, glycosylated hemoglobin level (HbA1C), lipid profile, renal function test and fundus examination were done before and during Escitalopram therapy.

RESULTS

A significant decline in mean HAM-D scores was observed 3 weeks onwards till the end of the study during Escitalopram therapy. There was a corresponding decline in mean fasting and post-prandial plasma glucose level at 6 and 12 weeks respectively and glycosylated hemoglobin level at 12 weeks was observed.

CONCLUSION

Escitalopram is effective in treating depression in patients with diabetes mellitus, and has beneficial effects on glycemic control.

Change over time in brain serotonin transporter binding in major depression: effects of therapy measured with [(123) I]-ADAM SPECT

Several studies have reported low brain serotonin transporter (SERT) binding in individuals with major depression. We hypothesized that the SERT standardized uptake ratio (SUR) values using [(123) I]-ADAM single photon emission computed tomography would increase in depressed subjects who responded to cognitive behavior therapy (CBT) compared to CBT nonresponders. [(123) I]-ADAM scans were acquired before and after 12 weeks of CBT from 20 depressed subjects and on two occasions 12 weeks apart from 10 nondepressed, healthy volunteers. The primary outcome measure was change over time in SUR values in the midbrain, medial temporal lobe, and basal ganglia regions. Depressed subjects demonstrated low pretreatment mean SUR values that significantly increased over time in the midbrain (P = .011), right medial temporal lobe (P = .008), and left medial temporal lobe (P = .000) regions. Treatment responders showed a significant increase over time in SUR values in left medial temporal lobe (P = .029) and right medial temporal lobe (P = .007) regions. Partial and nonresponder subjects also showed a significant increase over time in SUR values in the left medial temporal region (P = .040) (vs. healthy volunteers), but to a lesser degree. The findings suggest that low pretreatment SERT binding may increase over time in some depressed individuals who experience symptom improvement.

Serotonergic function and treatment of behavioral and psychological symptoms of frontotemporal dementia

OBJECTIVES

The purposes of this study were first, to evaluate the effectiveness of citalopram in treating behavioral disturbances in frontotemporal dementia (FTD) subjects and second, to determine whether an association exists between serotonergic function, as determined by a neuroendocrine challenge, and treatment response.

DESIGN

Single-dose citalopram (30 mg per os) challenge followed by a 6-week open-label study.

SETTING

Outpatients referred to memory clinics.

PARTICIPANTS

Fifteen patients suffering from FTD with severe behavioral and psychological symptoms of dementia.

INTERVENTION

Following citalopram challenge, all patients were treated with citalopram titrated to a target dose of 40 mg once daily.

MEASUREMENTS

Behavioral disturbances, using the Neuropsychiatric Inventory (NPI) (primary outcome) and Frontal Behavioural Inventory (secondary outcome), were assessed. Change in prolactin concentration following citalopram challenge was used as an index of central serotonergic response.

RESULTS

Citalopram treatment was effective in treating behavioral symptoms, with significant decreases in NPI total score (F[2, 28] = 6.644, p = 0.004), disinhibition (F[2, 28] = 4.030, p = 0.029), irritability (F[2, 28] = 7.497, p = 0.003) and depression (F[2, 28] = 3.467, p = 0.045) scores over the 6 weeks. Significant improvement in Frontal Behavioural Inventory scores suggested that citalopram was also effective in the treatment ofbehaviors specific to FTD. A lower change score in concentration of prolactin was significantly positively correlated with greater improvement in the total NPI score from baseline to endpoint (r = 0.687, p = 0.005). A blunted response to a citalopram challenge, implying a dysfunctional serotonergic system, predicted a more positive treatment outcome.

CONCLUSIONS

The results suggest that despite the endogenous serotonin deficiency of FTD, citalopram treatment may be effective in targeting the behavioral disturbances characteristic of FTD.

Translational evaluation of JNJ-18038683, a 5-hydroxytryptamine type 7 receptor antagonist, on rapid eye movement sleep and in major depressive disorder

In rodents 5-hydroxytryptamine type 7 (5-HT(7)) receptor blockade has been shown to be effective in models of depression and to increase the latency to rapid eye movement (REM) sleep and decrease REM duration. In the clinic, the REM sleep reduction observed with many antidepressants may serve as a biomarker. We report here the preclinical and clinical evaluation of a 5-HT(7) receptor antagonist, (3-(4-chlorophenyl)-1,4,5,6,7,8-hexahydro-1-(phenylmethyl)pyrazolo[3,4-d]azepine 2-hydroxy-1,2,3-propanetricarboxylate) (JNJ-18038683). In rodents, JNJ-18038683 increased the latency to REM sleep and decreased REM duration, and this effect was maintained after repeated administration for 7 days. The compound was effective in the mouse tail suspension test. JNJ-18038683 enhanced serotonin transmission, antidepressant-like behavior, and REM sleep suppression induced by citalopram in rodents. In healthy human volunteers JNJ-18038683 prolonged REM latency and reduced REM sleep duration, demonstrating that the effect of 5-HT(7) blockade on REM sleep translated from rodents to humans. Like in rats, JNJ-18038683 enhanced REM sleep suppression induced by citalopram in humans, although a drug-drug interaction could not be ruled out. In a double-blind, active, and placebo-controlled clinical trial in 225 patients suffering from major depressive disorder, neither treatment with pharmacologically active doses of JNJ-18038683 or escitalopram separated from placebo, indicating a failed study lacking assay sensitivity. Post hoc analyses using an enrichment window strategy, where all the efficacy data from sites with an implausible high placebo response [placebo group Montgomery-Åsberg Depression Rating Scale (MADRS) < = 12] and from sites with no placebo response (MADRS > = 28) are removed, there was a clinically meaningful difference between JNJ-18038683 and placebo. Further clinical studies are required to characterize the potential antidepressant efficacy of JNJ-18038683.

Short term vs. long term test-retest reproducibility of ¹²³I-ADAM for the binding of serotonin transporters in the human brain

Previous brain imaging studies have demonstrated a seasonal difference of serotonin transporter (SERT) binding in the human brain. However, the results were somewhat contradictory. We conducted test-retest study with single photon emission computed tomography (SPECT) with ¹²³I-ADAM as ligand in 28 healthy subjects. Ten of the subjects were studied within 1 month, whereas 18 were randomly assigned to be studied over a period of up to 1 year. The primary measure was the specific uptake ratio (SUR). Regions of interest included the midbrain, thalamus, putamen and caudate. The intra-class correlation coefficient (ICC) was 0.52-0.94 across different brain regions over 1 month, whereas the ICC was -0.24-0.63 over a 1-year period. The 1-month variability ranged from 6.5 ± 5.1% to 12.5 ± 10.6% across different brain regions, and the 1-year variability ranged from 16.5 ± 9.6% to 41.9 ± 35.5%. The Kruskal-Wallis test revealed a significant difference of variability across months. The Wilcoxon Signed Ranks Test showed the SUR between test-retest scans was of borderline significance. Curve fitting, using a 4th degree polynomial model, revealed a significant circadian correlation between the variability and interval of test-retest measurements. Our findings demonstrate the test-retest reproducibility of ¹²³I-ADAM in different time periods and suggest that circadian variation of SERT levels in the human brain might exist.

Effects of venlafaxine and escitalopram treatments on NMDA receptors in the rat depression model

Depression may relate to neurocognitive impairment that results from alteration of N-methyl-D: -aspartate receptor (NMDAR) levels. Venlafaxine and escitalopram are two drugs commonly used to treat depression. The drugs may affect expression of NMDARs, which mediate learning and memory formation. The aim of the study was to examine whether the effects of venlafaxine and escitalopram treatments are associated with NMDARs in a rat model of depression. Forty male Wistar albino rats were randomly divided into four groups (n = 10) as follows: control group, chronic mild stress group (CMS), venlafaxine (20 mg/kg body weight per day) + CMS, and escitalopram (10 mg/kg body weight per day) + CMS. After induction of depression, a decrease in the concentration of NR2B was observed; venlafaxine treatment prevented the reduction of NR2B expression. Escitalopram treatment did not effect the reduced levels of NR2B resulting from depression. There was no significant difference in NR2A concentration among groups. The present data support the notion that venlafaxine plays a role in maintaining NR2B receptor in experimental depression. It may be possible that treatment with escitalopram has no effect on NMDARs in experimental depression.

Effects of venlafaxine and escitalopram treatments on NMDA receptors in the rat depression model

Depression may relate to neurocognitive impairment that results from alteration of N-methyl-D: -aspartate receptor (NMDAR) levels. Venlafaxine and escitalopram are two drugs commonly used to treat depression. The drugs may affect expression of NMDARs, which mediate learning and memory formation. The aim of the study was to examine whether the effects of venlafaxine and escitalopram treatments are associated with NMDARs in a rat model of depression. Forty male Wistar albino rats were randomly divided into four groups (n = 10) as follows: control group, chronic mild stress group (CMS), venlafaxine (20 mg/kg body weight per day) + CMS, and escitalopram (10 mg/kg body weight per day) + CMS. After induction of depression, a decrease in the concentration of NR2B was observed; venlafaxine treatment prevented the reduction of NR2B expression. Escitalopram treatment did not effect the reduced levels of NR2B resulting from depression. There was no significant difference in NR2A concentration among groups. The present data support the notion that venlafaxine plays a role in maintaining NR2B receptor in experimental depression. It may be possible that treatment with escitalopram has no effect on NMDARs in experimental depression.

5-HT radioligands for human brain imaging with PET and SPECT

The serotonergic system plays a key modulatory role in the brain and is the target for many drug treatments for brain disorders either through reuptake blockade or via interactions at the 14 subtypes of 5-HT receptors. This review provides the history and current status of radioligands used for positron emission tomography (PET) and single photon emission computerized tomography (SPECT) imaging of human brain serotonin (5-HT) receptors, the 5-HT transporter (SERT), and 5-HT synthesis rate. Currently available radioligands for in vivo brain imaging of the 5-HT system in humans include antagonists for the 5-HT(1A), 5-HT(1B), 5-HT(2A), and 5-HT(4) receptors, and for SERT. Here we describe the evolution of these radioligands, along with the attempts made to develop radioligands for additional serotonergic targets. We describe the properties needed for a radioligand to become successful and the main caveats. The success of a PET or SPECT radioligand can ultimately be assessed by its frequency of use, its utility in humans, and the number of research sites using it relative to its invention date, and so these aspects are also covered. In conclusion, the development of PET and SPECT radioligands to image serotonergic targets is of high interest, and successful evaluation in humans is leading to invaluable insight into normal and abnormal brain function, emphasizing the need for continued development of both SPECT and PET radioligands for human brain imaging.

Loudness dependence of auditory evoked potentials (LDAEP) correlates with the availability of dopamine transporters and serotonin transporters in healthy volunteers-a two isotopes SPECT study

RATIONALE AND OBJECTIVE

Although loudness dependence of auditory evoked potentials (LDAEPs) had been suggested as a noninvasive measure of central serotonin functions, recent studies suggest that LDAEP may be modulated by multiple neuromodulatory systems, such as dopamine. Here, we explore the relationship between LDAEP and dopamine and serotonin in the level of monoamine transporter availability.

METHODS

Forty-nine healthy volunteers received LDAEP and single-photon emission computed tomography (SPECT) using [(99m)Tc] TRODAT and [(123)I] ADAM to approximate the availability of dopamine transporters (DATs) and serotonin transporters (SERTs).

RESULTS

LDAEP was found to be positively associated with DAT, after adjusting for age and gender, and the log-transformed slope of loudness dependence at Cz was negatively associated with SERT.

CONCLUSION

Our findings provide further evidence for the possible involvement of dopamine and serotonins in the genesis of LDAEP.

Distribution volume ratio of serotonin and dopamine transporters in euthymic patients with a history of major depression - a dual-isotope SPECT study

Serotonin transporter (SERT) and dopamine transporter (DAT) levels differ in patients with major depression who are in a depressed state in comparison with healthy controls. The aim of this study was to examine the distribution volume ratios (DVRs) of SERT and DAT in drug-free and euthymic patients with a history of major depression. Subjects comprised 13 patients with a history of major depression and 26 sex- and age-matched healthy controls. The euthymic state of depression was defined as a score of 7 or less on the Hamilton Depression Rating Scale. The DVRs of SERT and DAT were approximated using SPECT, with [(123)I] 2-((2-((dimethylamino)methyl)phenyl)thio)-5-iodophenylamine (ADAM) and [(99m)Tc] TRODAT-1 as the ligands, respectively. There were no significant differences in the DVRs of SERT or DAT between healthy subjects and euthymic patients with a history of major depression; hence, the SERT and DAT DVRs may not therefore be trait markers for patients with major depression, which helps us to understand more about the pathophysiology of depression.

Escitalopram: a review of its use in the management of major depressive disorder in adults

Escitalopram (escitalopram oxalate; Cipralex, Lexapro), a selective serotonin reuptake inhibitor (SSRI) indicated for the treatment of major depressive disorder (MDD), demonstrates a highly selective and potent, dose-dependent inhibition of the human serotonin transporter, inhibiting serotonin reuptake into presynaptic nerve terminals and thus increasing serotonergic activity in the CNS. With regard to primary endpoints (such as improved scores on the Montgomery-Asberg Depression Rating Scale [MADRS] and the Hamilton Depression Rating Scale [HAM-D]), escitalopram was generally more effective than placebo, at least as effective as citalopram, and generally at least as effective as other comparator drugs, including the SSRIs fluoxetine, paroxetine and sertraline, the serotonin-noradrenaline (norepinephrine) reuptake inhibitors (SNRIs) venlafaxine extended release and duloxetine, and the aminoketone bupropion in adult patients with MDD in short-term, well designed trials. Moreover, it demonstrated a rapid onset of antidepressant action. Escitalopram was also found to be cost effective in several studies, dominating other SSRIs and venlafaxine extended release. Maintenance therapy is commonly required to prevent recurrence of depression. Long-term trials corroborated short-term results, with escitalopram demonstrating greater efficacy than placebo in relapse prevention. Additionally, escitalopram was at least as effective as citalopram, paroxetine and duloxetine in long-term comparative trials. Escitalopram has a predictable tolerability profile with generally mild to moderate and transient adverse events, and a low propensity for drug interactions. Sexual dysfunction with escitalopram treatment appeared to occur to a similar or lower extent to that with paroxetine (another SSRI), to a similar or greater extent to that with the SNRI duloxetine, and to a greater extent than that with the aminoketone bupropion. Thus, escitalopram is an effective and generally well tolerated treatment for moderate to severe MDD. Escitalopram, like other SSRIs, is an effective first-line option in the management of patients with MDD.

Escitalopram causes fewer seizures in human overdose than citalopram

CONTEXT

Seizures are a recognized complication of acute overdose with the racemic (1:1 ratio of R- and S-enantiomers) selective serotonin reuptake inhibitor antidepressant citalopram.

OBJECTIVE

We tested the hypothesis that escitalopram (the therapeutically active S-enantiomer of citalopram) causes fewer seizures in overdose than citalopram at comparable doses of the S-enantiomer.

METHODS

Multicenter retrospective review of cases with citalopram and escitalopram overdose reported to German, Austrian, and Swiss Poisons Centers between 1997 and 2006.

RESULTS

316 citalopram and 63 escitalopram cases were analyzed. Somnolence, nausea, vomiting, tachycardia, QT prolongation, and tremor occurred with similar frequency in both groups. There was a striking difference in the frequency of single and multiple seizures: 43 cases (13.5%) in the citalopram group and 1 case (1.6%) with a single seizure in the escitalopram group (p=0.0065).

DISCUSSION AND CONCLUSIONS

At comparable ingested doses of the S-enantiomer, the symptom profile for citalopram and escitalopram intoxications is similar except for seizures that occur more frequently in citalopram than in escitalopram poisoning.

Why do some promising brain-stimulation devices fail the next steps of clinical development?

Interest in techniques of noninvasive brain stimulation (NIBS) has been growing exponentially in the last decade. Recent studies have shown that some of these techniques induce significant neurophysiological and clinical effects. Although recent results are promising, there are several techniques that have been abandoned despite positive initial results. In this study, we performed a systematic review to identify NIBS methods with promising preliminary clinical results that were not fully developed and adopted into clinical practice, and discuss its clinical, research and device characteristics. We identified five devices (transmeatal cochlear laser stimulation, transcranial micropolarization, transcranial electrostimulation, cranial electric stimulation and stimulation with weak electromagnetic fields) and compared them with two established NIBS devices (transcranial magnetic stimulation and transcranial direct current stimulation) and with well-known drugs used in neuropsychiatry (pramipexole and escitalopram) in order to understand the reasons why they failed to reach clinical practice and further steps of research development. Finally, we also discuss novel NIBS devices that have recently showed promising results: brain ultrasound and transcranial high-frequency random noise stimulation. Our results show that some of the reasons for the failure of NIBS devices with promising clinical findings are the difficulty to disseminate results, lack of controlled studies, duration of research development, mixed results and lack of standardization.

Differential effects of escitalopram on attention: a placebo-controlled, double-blind cross-over study

RATIONALE

The role of serotonin (5-HT) in attention is not fully understood yet.

OBJECTIVE

We aimed to investigate whether attention is modulated after treatment with escitalopram, a selective serotonin reuptake inhibitor (SSRI).

METHODS

We administered 10 mg of escitalopram to 20 healthy subjects in a placebo-controlled, double-blind cross-over design for 1 day or to another 20 participants for a period of 7 days. Attention was assessed at time of plasma peak escitalopram concentration using the computerised Attention Network Test (ANT), which is a combined flanker and cued reaction time task.

RESULTS

The results showed differential effects of serotonergic manipulation on attention depending on sequence of intake. For the acute treatment, we found significant differences between escitalopram and placebo for all warning conditions dependent of sequence of intake: participants receiving escitalopram as first treatment showed significant slower reaction times in all warning conditions as compared with placebo while participants receiving escitalopram as second treatment showed significant faster reaction times as compared with placebo. For the sub-chronic treatment, we found significant differences between escitalopram and placebo depending on sequence of intake, but only for the flanker condition: participants receiving escitalopram first had significant slower reaction times in incongruent trials with escitalopram as compared with placebo while participants starting with placebo had significant shorter reaction times in incongruent trials with escitalopram.

CONCLUSIONS

Thus, the results showed a differential effect of escitalopram in cognition, especially in attention, and are discussed with regard to an interaction between serotonin and familiarity with the attention test.

Area-specific modulation of neural activation comparing escitalopram and citalopram revealed by pharmaco-fMRI: a randomized cross-over study

Area-specific and stimulation-dependent changes of human brain activation by selective serotonin reuptake inhibitors (SSRI) are an important issue for improved understanding of treatment mechanisms, given the frequent prescription of these drugs in depression and anxiety disorders. The aim of this neuroimaging study was to investigate differences in BOLD-signal caused by administration of the SSRIs escitalopram and citalopram using pharmacological functional magnetic resonance imaging (pharmaco-fMRI). Eighteen healthy subjects participated in a placebo-controlled, randomized, double-blind study in cross-over repeated measures design. Each volunteer performed facial emotional discrimination and a sensorimotor control paradigm during three scanning sessions. Citalopram (20 mg/d), escitalopram (10 mg/d) and placebo were administered for 10 days each with a drug-free period of at least 21 days. Significant pharmacological effects on BOLD-signal were found in the amygdala, medial frontal gyrus, parahippocampal, fusiform and middle temporal gyri. Post-hoc t-tests revealed decreased BOLD-signal in the right amygdala and left parahippocampal gyrus in both pharmacological conditions, compared to placebo. Escitalopram, compared to citalopram, induced a decrease of BOLD-signal in the medial frontal gyrus and an increase in the right fusiform and left parahippocampal gyri. Drug effects were concentrated in brain regions with dense serotonergic projections. Both escitalopram and citalopram attenuated BOLD-signal in the amygdala and parahippocampal cortex to emotionally significant stimuli compared to control stimuli. We believe that reduced reactivity in the medial frontal gyrus found for escitalopram compared to citalopram administration might explain the response differences between study drugs as demonstrated in previous clinical trials.

Subchronic SSRI administration reduces insula response during affective anticipation in healthy volunteers

The anterior cingulate cortex (ACC) and insula are important neural substrates for the integration of cognitive, emotional, and physiological information, as well as the coordination of responses to anticipated stimuli. Increased neural activation within these structures has been observed in individuals with anxiety and depressive disorders. Selective serotonin reuptake inhibitors (SSRIs) are among the most effective and frequently prescribed anxiolytic agents, yet it is not known whether ACC or insula underlie the effects of these drugs. We examined whether subchronic administration of a SSRI to healthy volunteers attenuates activation in ACC or insula during anticipation, an important emotional process underlying anxiety. Support for this hypothesis would help to understand where and by what process SSRIs may exert beneficial effects as anxiolytics and would provide further mechanistic evidence for functional magnetic resonance imaging (fMRI) as a biomarker for the development of anxiolytics. Fifteen volunteers participated in a double-blind, placebo-controlled, randomized cross-over study. Participants completed a pleasant and aversive picture-cued anticipation task during fMRI after taking either escitalopram (10 mg) or placebo for 21 d. We found that escitalopram significantly decreased activation in bilateral posterior and middle insula during the anticipation condition irrespective of stimulus valence and in medial prefrontal and ACC during anticipation of aversive vs. pleasant images. Reduced insular and ACC activation in healthy controls during anticipation may be integral to the therapeutic efficacy of SSRIs and may provide a mechanistic approach for the use of pharmaco-fMRI in the identification of novel pharmacotherapeutic agents in patient populations.

Portal infusion of escitalopram enhances hepatic glucose disposal in conscious dogs

To examine whether escitalopram enhances net hepatic glucose uptake during a hyperinsulinemic hyperglycemic clamp, studies were performed in conscious 42-h-fasted dogs. The experimental period was divided into P1 (0-90 min) and P2 (90-270 min). During P1 and P2 somatostatin (to inhibit insulin and glucagon secretion), 4x basal intraportal insulin, basal intraportal glucagon, and peripheral glucose (2x hepatic glucose load) were infused. Saline was infused intraportally during P1 in all groups. In one group saline infusion was continued in P2 (SAL, n = 11), while escitalopram was infused intraportally at 2 microg/kg/min (L-ESC, n = 6) or 8 microg/kg/min (H-ESC, n = 7) during P2 in two other groups. The arterial insulin concentrations rose approximately four fold (to 123 +/- 8, 146 +/- 13 and 148 +/- 15 pmol/L) while glucagon concentrations remained basal (41 +/- 3, 44 +/- 9 and 40 +/- 3 ng/L) in all groups. The hepatic glucose load averaged 216 +/- 13, 223 +/- 19 and 202 +/- 12 micromol/kg/min during the entire experimental period (P1 and P2) in the SAL, L-ESC and H-ESC groups, respectively. Net hepatic glucose uptake was 11.6 +/- 1.4, 10.1 +/- 0.9 and 10.4 +/- 2.3 micromol/kg/min in P1 and averaged 16.9 +/- 1.5, 15.7 +/- 1.3 and 22.6 +/- 3.7 (P < 0.05) in the SAL, L-ESC and H-ESC groups, respectively during the last hour of P2 (210-270 min). Net hepatic carbon retention (glycogen storage) was 15.4 +/- 1.3, 14.9 +/- 0.6 and 20.9 +/- 2.6 (P < 0.05) micromol/kg/min in SAL, L-ESC and H-ESC respectively during the last hour of P2. Escitalopram enhanced net hepatic glucose uptake and hepatic glycogen deposition, showing that it can improve hepatic glucose clearance under hyperinsulinemic hyperglycemic conditions. Its use in individuals with diabetes may, therefore, result in improved glycemic control.

Differences in the dynamics of serotonin reuptake transporter occupancy may explain superior clinical efficacy of escitalopram versus citalopram

Escitalopram the S-enantiomer of the racemate citalopram, is clinically more effective than citalopram in the treatment of major depressive disorder. However, the precise mechanism by which escitalopram achieves superiority over citalopram is yet to be determined. It has been hypothesized that the therapeutically inactive R-enantiomer competes with the serotonin-enhancing S-enantiomer at a low-affinity allosteric site on serotonin reuptake transporters (SERTs), and reduces the effectiveness of the S-enantiomer at the primary, high-affinity serotonin-binding site. This study summarizes the results of two recent single-photon emission computerized tomography studies measuring SERT occupancy in citalopram-treated and escitalopram-treated healthy volunteers, after a single dose and multiple doses (i.e. under steady-state conditions). The single-dose study showed no attenuating effect of R-citalopram. After multiple dosing, however, SERT occupancy was significantly reduced in the presence of R-citalopram. Under steady-state conditions, R-enantiomer concentrations were greater than for the S-enantiomer because of slower clearance of R-citalopram. A pooled analysis suggests that build-up of the R-enantiomer after repeated citalopram dosing may lead to increased inhibition of S-enantiomer occupancy of SERT. This review adds to the growing body of evidence regarding differences in the dynamics of SERT occupancy, that is, molecular mechanisms underlying the often-observed superior clinical efficacy of escitalopram compared with citalopram in major depressive disorder.

Imaging the serotonin transporter using (123)I-ADAM in the human brain

The aim of this study was to examine the feasibility of (123)I-ADAM to image the serotonin transporter (SERT) in Asian (Taiwanese) subjects. Single photon emission computed tomography (SPECT) scans were performed on nine healthy volunteers who were s-allele carriers at the polymorphism within the serotonin transporter promoter region (SERTPR) after intravenous bolus injection of (123)I-ADAM. Quantification of (123)I-ADAM binding was performed using the ratio equilibrium method (REM) with specific uptake ratio (SUR) and a simplified reference tissue model (SRTM). Curve-fitting techniques were used to obtain the peak equilibrium point from 241 to 301 min (average 264+/-20 min) after injection of (123)I-ADAM for the midbrain and from 215 to 270 min (average 235+/-18 min) after injection of (123)I-ADAM for the striatum. Two sets of SUR were obtained by either curve fitting (estimated values) or integrated period from 240 to 270 min (observed values). The estimated values of SUR were 2.11+/-0.51 for the midbrain and 1.50+/-0.44 for the striatum, whereas the observed values were 2.11+/-0.83 for the midbrain and 1.24+/-0.31 for the striatum. The SRTM showed that the binding potential (BP) was 2.10+/-0.66 for the midbrain and 1.35+/-0.25 for the striatum. There was a good correlation between estimated SUR, observed SUR and SRTM in the midbrain but not in the striatum. The optimal scanning duration for both the midbrain and the striatum should be 220 to 280 min similar to that suggested by previous studies in Caucasians. However, due to the low signal-to-noise ratio in the striatum, (123)I-ADAM could be an ideal tracer for imaging SERT in the midbrain but not in the striatum.

Evidence why paroxetine dose escalation is not effective in major depressive disorder: a randomized controlled trial with assessment of serotonin transporter occupancy

Dose escalation is often used in depressed patients who fail to respond to standard doses of selective serotonin reuptake inhibitors, but clinical efficacy is equivocal. We aimed to reassess the efficacy of paroxetine dose escalation and quantify whether paroxetine dose escalation increases occupancy of the serotonin transporter (SERT) more than placebo dose escalation in a randomized controlled trial. We recruited 107 nonpsychotic, unipolar depressed outpatients (18-70 years; Hamilton Depression Rating Scale (HDRS(17)) >18) from primary care and psychiatric outpatient departments. After 6 weeks, open-label paroxetine 20 mg per day (T0), nonresponding patients (HDRS(17) decrease <50%; n=60) were randomized to double-blind paroxetine (30-50 mg per day as tolerable) or placebo dose escalation (paroxetine 20 mg per day+placebo). Patients were followed until 6 weeks after randomization (T1). Forty-nine patients, drug free at study entry, underwent single-photon emission-computed tomography (SPECT) scanning before treatment and were scanned repeatedly at T0 and T1. Paroxetine serum concentrations and SERT occupancy were determined at T0 and T1 (n=32). We terminated the dose-escalation trial after an interim analysis. Thirty nonresponding patients were randomized to paroxetine (46.7+/-5.5 mg per day), 27 to placebo dose escalation. Response rates were 10/30 (33.3%) and 10/27 (37.0%), respectively. Repeated measurement analyses showed no significant effect for treatment (p=0.88, exceeding a priori stopping rules for futility (p>0.5)). Overall dropout was higher for placebo (26.7%) than paroxetine (3.3%; p=0.03). Paroxetine dose escalation increased paroxetine serum concentrations (p<0.001). SPECT measurements (12 patients randomized to paroxetine (46.9+/-4.8 mg) and 14 to placebo dose escalation) showed no significant increase of midbrain SERT occupancy (2.5+/-26.4%, paroxetine; 3.1+/-25.8% placebo; p=0.687) nor in diencephalon (p=0.529). Paroxetine dose escalation in depressed patients has no clinical benefit over placebo dose escalation. This is explained by the absence of significant increases of SERT occupancy by paroxetine dose escalation, despite increased paroxetine serum concentrations (ISRCTN44111488).

Divergent effects of increased serotonergic activity on psychophysiological parameters of human attention

Selective serotonin reuptake inhibitors (SSRIs) are frequently combined to the antipsychotic medication of schizophrenia patients, to treat their depressed, cognitive or negative symptoms. No convincing neurochemical theory exists for this combination. The role of serotonin in those psychophysiological parameters of attention that are already found to be disturbed in schizophrenia, e.g. processing negativity (PN), mismatch negativity (MMN) and P300 amplitude, is poorly understood. In the present study the effects of increased serotonergic activity on these psychophysiological parameters is investigated. In a balanced, double-blind, placebo-controlled, cross-over experiment 18 healthy male volunteers received an oral dose of either placebo or of 10 mg escitalopram (a highly specific SSRI) on two separate test days, after which they were tested in an auditory selective attention paradigm and a MMN paradigm. Escitalopram significantly increased PN and MMN compared to placebo, without affecting the P300 amplitude. Furthermore, administration of escitalopram resulted in a small, yet significant, reduction of task performance in the selective attention paradigm compared to placebo, while it did not affect reaction time. Contrary to what was expected, escitalopram enhanced PN and MMN, without affecting the P300 amplitude. The results are discussed in the light of dosage issues and subtypes of serotonergic receptors.

Escitalopram for the treatment of major depression and anxiety disorders

Escitalopram is the S-enantiomer of the selective serotonin reuptake inhibitor (SSRI) citalopram, which contains equal amounts of the S- and R-forms in a racemic mixture. Escitalopram is the most selective SSRI, with almost no significant affinity to other tested receptors. It has been demonstrated that it is escitalopram that carries the therapeutic potential of citalopram, and has statistically superior and clinically relevant properties compared with citalopram. Escitalopram is at least as effective in the treatment of depression and anxiety as other SSRIs, as well as venlafaxine, bupropion and duloxetine. Owing to multiple metabolic degrading pathways, the clinically relevant interactions of escitalopram with other drugs are minimal. Compared with other antidepressants, escitalopram is generally better tolerated, its onset of action is relatively fast, and its use may have cost-effectiveness and cost-utility advantages. Escitalopram is an effective first-line option in the management of patients with major depression, including severe forms, and various anxiety disorders.

123I-ADAM SPECT imaging of serotonin transporter binding in patients with night eating syndrome: a preliminary report

Night eating syndrome (NES) represents a delay in the circadian pattern of food intake, manifested by evening hyperphagia and/or nocturnal awakenings accompanied by ingestions of food. A neurobiological marker of NES has been implicated with the recently discovered therapeutic response to the selective serotonin reuptake inhibitor (SSRI) sertraline. This pilot SPECT (single photon emission computed tomography) study compared the serotonin transporter (SERT) uptake ratios of night eaters with those of healthy controls. Six night eaters underwent SPECT imaging using the radiopharmaceutical (123)I-ADAM. Uptake, compared with that of the cerebellum, was obtained for the midbrain, basal ganglia, and temporal lobes; uptake ratios in night eaters were compared with those of six healthy controls. Night eaters had significantly greater SERT uptake ratios in the midbrain than healthy controls. These findings, in conjunction with the therapeutic response of NES to sertraline, indicate that the serotonin system is involved in the pathophysiology of NES.