Lu AA21004, a novel multimodal antidepressant, produces regionally selective increases of multiple neurotransmitters--a rat microdialysis and electrophysiology study

A randomized, double-blind, duloxetine-referenced study comparing efficacy and tolerability of 2 fixed doses of vortioxetine in the acute treatment of adults with MDD

RATIONALE

Vortioxetine has reduced depressive symptoms in adults with major depressive disorder (MDD) in multiple clinical trials.

OBJECTIVES

The aim of this study is to evaluate the efficacy, safety, and tolerability of vortioxetine 15 and 20 mg vs placebo in adults with MDD.

METHODS

Patients were randomized 1:1:1:1 to vortioxetine 15 mg, vortioxetine 20 mg, duloxetine 60 mg (active reference), or placebo. The primary efficacy endpoint was mean change in Montgomery-Åsberg Depression Rating Scale (MADRS) total score at week 8 (MMRM). Safety/tolerability assessments included physical examinations, vital signs, laboratory evaluations, electrocardiograms, adverse events (AEs), Columbia-Suicide Severity Rating Scale, Arizona Sexual Experiences Scale, and Discontinuation-Emergent Signs and Symptoms checklist.

RESULTS

Six hundred and fourteen patients were randomized. Mean changes in MADRS scores were -12.83 (±0.834), -14.30 (±0.890), -15.57 (±0.880), and -16.90 (±0.884) for placebo, vortioxetine 15 mg (P = .224), vortioxetine 20 mg (P = .023), and duloxetine 60 mg (P < .001) (P vs placebo), respectively. AEs reported by ≥5 % of vortioxetine patients included nausea, headache, diarrhea, dizziness, dry mouth, constipation, vomiting, insomnia, fatigue, and upper respiratory infection. Treatment-emergent sexual dysfunction, suicidal ideation or behavior, and discontinuation symptoms were not significantly different between vortioxetine and placebo.

CONCLUSIONS

Vortioxetine 20 mg significantly reduced MADRS total scores after 8 weeks of treatment. Both vortioxetine doses were well tolerated.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT01153009; www.clinicaltrials.gov/ .

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.

Vortioxetine restores reversal learning impaired by 5-HT depletion or chronic intermittent cold stress in rats

Current treatments for depression, including serotonin-specific reuptake inhibitors (SSRIs), are only partially effective, with a high incidence of residual symptoms, relapse, and treatment resistance. Loss of cognitive flexibility, a component of depression, is associated with dysregulation of the prefrontal cortex. Reversal learning, a form of cognitive flexibility, is impaired by chronic stress, a risk factor for depression, and the stress-induced impairment in reversal learning is sensitive to chronic SSRI treatment, and is mimicked by serotonin (5-HT) depletion. Vortioxetine, a novel, multimodal-acting antidepressant, is a 5-HT3, 5-HT7 and 5-HT1D receptor antagonist, a 5-HT1B receptor partial agonist, a 5-HT1A receptor agonist, and inhibits the 5-HT transporter. Using adult male rats, we first investigated the direct effects of vortioxetine, acting at post-synaptic 5-HT receptors, on reversal learning that was compromised by 5-HT depletion using 4-chloro-DL-phenylalanine methyl ester hydrochloride (PCPA), effectively eliminating any contribution of 5-HT reuptake blockade. PCPA induced a reversal learning impairment that was alleviated by acute or sub-chronic vortioxetine administration, suggesting that post-synaptic 5-HT receptor activation contributes to the effects of vortioxetine. We then investigated the effects of chronic dietary administration of vortioxetine on reversal learning that had been compromised in intact animals exposed to chronic intermittent cold (CIC) stress, to assess vortioxetine's total pharmacological effect. CIC stress impaired reversal learning, and chronic vortioxetine administration prevented the reversal-learning deficit. Together, these results suggest that the direct effect of vortioxetine at 5-HT receptors may contribute to positive effects on cognitive flexibility deficits, and may enhance the effect of 5-HT reuptake blockade.

A randomized, double-blind, placebo-controlled study of vortioxetine on cognitive function in depressed adults

The efficacy of vortioxetine 10 and 20 mg/d vs. placebo on cognitive function and depression in adults with recurrent moderate-to-severe major depressive disorder (MDD) was evaluated. Patients (18-65 yr, N = 602) were randomized (1:1:1) to vortioxetine 10 or 20 mg/d or placebo for 8 wk in a double-blind multi-national study. Cognitive function was assessed with objective neuropsychological tests of executive function, processing speed, attention and learning and memory, and a subjective cognitive measure. The primary outcome measure was change from baseline to week 8 in a composite z-score comprising the Digit Symbol Substitution Test (DSST) and Rey Auditory Verbal Learning Test (RAVLT) scores. Depressive symptoms were assessed using the Montgomery-Åsberg Depression Rating Scale (MADRS). In the pre-defined primary efficacy analysis, both doses of vortioxetine were significantly better than placebo, with mean treatment differences vs. placebo of 0.36 (vortioxetine 10 mg, p < 0.0001) and 0.33 (vortioxetine 20 mg, p < 0.0001) on the composite cognition score. Significant improvement vs. placebo was observed for vortioxetine on most of the secondary objectives and subjective patient-reported cognitive measures. The differences to placebo in the MADRS total score at week 8 were -4.7 (10 mg: p < 0.0001) and -6.7 (20 mg: p < 0.0001). Path and subgroup analyses indicate that the beneficial effect of vortioxetine on cognition is largely a direct treatment effect. No safety concern emerged with vortioxetine. Vortioxetine significantly improved objective and subjective measures of cognitive function in adults with recurrent MDD and these effects were largely independent of its effect on improving depressive symptoms.

A review of the clinical efficacy, safety and tolerability of the antidepressants vilazodone, levomilnacipran and vortioxetine

INTRODUCTION

As a leading cause of disability, major depressive disorder (MDD) is characterized by reduced quality of life and altered functioning. Current pharmaceutical treatment options are limited in their success by modest effects and adverse events that often lead to discontinuation. One current trend in antidepressant development is to combine inhibition of the serotonin transporter with other pharmacological targets, including the norepinephrine transporter or different serotonin receptors.

AREAS COVERED

In a span of < 3 years, the FDA approved three new antidepressants for the treatment of MDD: vilazodone in January 2011, levomilnacipran in July 2013 and vortioxetine in September 2013. This article reviews the efficacy, safety and tolerability of these three drugs mainly from the Phase III trial data.

EXPERT OPINION

All three drugs are effective in the treatment of MDD, but data comparing them to other antidepressants is currently lacking. Vilazodone was proposed to produce a more rapid onset and have fewer sexual side effects but neither effect has been conclusively shown. Levomilnacipran appears to be effective in improving functional impairment, including both social and work functioning. Vortioxetine is currently the only drug of the three with proven efficacy in elderly patients. It also appears to have cognitive enhancing properties which are largely independent of improved depressive symptoms. Overall, these drugs represent a promising step forward in antidepressant drug development.

Vortioxetine: a review of its use in major depressive disorder

Vortioxetine (Brintellix(®)) is a serotonin (5-HT) transporter inhibitor that also acts on several 5-HT receptors, such as the 5-HT3 and 5-HT1A receptors. It is approved in the US and the EU for the treatment of adult patients with major depressive disorder (MDD); this article reviews the pharmacological properties of oral vortioxetine and its clinical efficacy and tolerability in these patients. Vortioxetine is generally efficacious in patients with MDD in acute treatment trials (including elderly patients), in a relapse-prevention trial, and in open-label extension trials. It is associated with improved cognitive function in patients with MDD; this does not occur solely via improvement in depressive symptom severity. It is well tolerated, but is associated with significantly increased sexual dysfunction at the highest dosage; however, vortioxetine was shown to improve previous-treatment-emergent sexual dysfunction in patients with well-treated MDD to a greater degree than escitalopram. Vortioxetine extends the available treatment options for patients with MDD, and further investigation into its comparative efficacy versus other antidepressants will allow for more accurate placement among these treatment options.

Pharmacology and clinical potential of vortioxetine in the treatment of major depressive disorder

VORTIOXETINE IS A NEW MULTIMODAL ACTION ANTIDEPRESSANT WITH TWO TYPES OF ACTION: serotonin transporter (SERT) blockade and a strong affinity for several serotoninergic receptors. It is an antagonist of the 5-HT3 and 5-HT7 receptors, a partial agonist of 5-HT1B, and an agonist of 5-HT1A. Its combined action on SERT and four subtypes of serotoninergic receptors increases the extracellular concentration of serotonin, dopamine, and noradrenaline. Twelve clinical trials have been carried out, nine of which had positive results versus placebo. When active comparators were included in the study design, no significant differences were found except in one study in which the efficacy of vortioxetine was superior to the comparator (agomelatine) in depression resistant to selective serotonin reuptake inhibitors (SSRI)/serotonin-norepinephrine reuptake inhibitors (SNRI) treatment. Tolerability studies indicate that the drug does not cause any important problems on blood tests, vital signs, or on electrocardiography. The lack of weight gain and induction of metabolic syndrome and the lack of significant changes in the QTc are especially important. The incidence rate of sexual dysfunction is low and similar to placebo in various trials. Similarly, cognitive function remains intact with vortioxetine.

Serotonergic modulation of glutamate neurotransmission as a strategy for treating depression and cognitive dysfunction

Monoamine-based treatments for depression have evolved greatly over the past several years, but shortcomings such as suboptimal efficacy, treatment lag, and residual cognitive dysfunction are still significant. Preclinical and clinical studies using compounds directly targeting glutamatergic neurotransmission present new opportunities for antidepressant treatment, with ketamine having a surprisingly rapid and sustained antidepressant effect that is presumably mediated through glutamate-dependent mechanisms. While direct modulation of glutamate transmission for antidepressant and cognition-enhancing actions may be hampered by nonspecific effects, indirect modulation through the serotonin (5-HT) system may be a viable alternative approach. Based on localization and function, 5-HT can modulate glutamate neurotransmission at least through the 5-HT1A, 5-HT1B, 5-HT3, and 5-HT7 receptors, which presents a rational pharmacological opportunity for modulating glutamatergic transmission without the direct use of glutamatergic compounds. Combining one or more of these glutamate-modulating 5-HT targets with 5-HT transporter inhibition may offer new therapeutic opportunities. The multimodal compounds vortioxetine and vilazodone are examples of this approach with diverse mechanisms, and their different clinical effects will provide valuable insights into serotonergic modulation of glutamate transmission for the potential treatment of depression and associated cognitive dysfunction.

New generation multi-modal antidepressants: focus on vortioxetine for major depressive disorder

Vortioxetine is a novel antidepressant with effects on multiple 5-HT receptors and on the serotonin transporter. This paper reviews preclinical and clinical evidence regarding its mechanism of action, its tolerability, and its efficacy in treating major depression. Clinical studies indicate that vortioxetine is effective in the treatment of major depression, though there is no suggestion of superiority over active comparators. There may be a clinically meaningful advantage in terms of tolerability.

Vortioxetine, but not escitalopram or duloxetine, reverses memory impairment induced by central 5-HT depletion in rats: evidence for direct 5-HT receptor modulation

Depressed patients suffer from cognitive dysfunction, including memory deficits. Acute serotonin (5-HT) depletion impairs memory and mood in vulnerable patients. The investigational multimodal acting antidepressant vortioxetine is a 5-HT3, 5-HT7 and 5-HT1D receptor antagonist, 5-HT1B receptor partial agonist, 5-HT1A receptor agonist and 5-HT transporter (SERT) inhibitor that enhances memory in normal rats in novel object recognition (NOR) and conditioned fear (Mørk et al., 2013). We hypothesized that vortioxetine's 5-HT receptor mechanisms are involved in its memory effects, and therefore investigated these effects in 5-HT depleted rats. Four injections of the irreversible tryptophan hydroxylase inhibitor 4-chloro-dl-phenylalanine methyl ester hydrochloride (PCPA, 86mg/kg, s.c.) induced 5-HT depletion, as measured in hippocampal homogenate and microdialysate. The effects of acute challenge with vortioxetine or the 5-HT releaser fenfluramine on extracellular 5-HT were measured in PCPA-treated and control rats. PCPA's effects on NOR and spontaneous alternation (SA) performance were assessed along with the effects of acute treatment with 5-hydroxy-l-tryptophan (5-HTP), vortioxetine, the selective 5-HT reuptake inhibitor escitalopram, or the 5-HT norepinephrine reuptake inhibitor duloxetine. SERT occupancies were estimated by ex vivo autoradiography. PCPA depleted central 5-HT by >90% in tissue and microdialysate, and impaired NOR and SA performance. Restoring central 5-HT with 5-HTP reversed these deficits. At similar SERT occupancies (>90%) vortioxetine, but not escitalopram or duloxetine, restored memory performance. Acute fenfluramine significantly increased extracellular 5-HT in control and PCPA-treated rats, while vortioxetine did so only in control rats. Thus, vortioxetine restores 5-HT depletion impaired memory performance in rats through one or more of its receptor activities.

A randomized, double-blind, fixed-dose study comparing the efficacy and tolerability of vortioxetine 2.5 and 10 mg in acute treatment of adults with generalized anxiety disorder

BACKGROUND

Vortioxetine is a recently approved multimodal antidepressant with anxiolytic properties in preclinical studies.

OBJECTIVE

This double-blind, placebo-controlled study assessed the efficacy and tolerability of vortioxetine in subjects with a primary diagnosis of generalized anxiety disorder.

METHODS

Subjects (n = 457) were randomized 1:1:1 to treatment with placebo or vortioxetine 2.5 or 10 mg once daily. The primary efficacy endpoint was reduction in Hamilton Anxiety Scale (HAM-A) total scores from baseline after 8 weeks of treatment. Key secondary outcomes were changes from baseline in HAM-A total scores for the 2.5 and 10 mg dose, Hospital Anxiety and Depression anxiety subscore, 36-Item Short-Form Health Survey, Sheehan Disability Scale, and Clinical Global Impression-Improvement Scale score, as well as HAM-A response rate at week 8.

RESULTS

Neither vortioxetine dose achieved a statistically significant improvement over placebo on the primary endpoint (least-squares mean difference ± standard error from placebo: -0.87 ± 0.803 [p = 0.279] for 2.5 mg and -0.81 ± 0.791 [p = 0.306] for 10 mg vortioxetine) or on any secondary efficacy endpoints. Common adverse events (≥5% in either vortioxetine group) were nausea, dry mouth, headache, diarrhea, constipation, and vomiting.

CONCLUSIONS

Vortioxetine 2.5 and 10 mg treatment did not significantly improve generalized anxiety disorder symptoms versus placebo. Vortioxetine was safe and well tolerated in this patient population.

A randomised, double-blind, placebo-controlled, duloxetine-referenced study of the efficacy and tolerability of vortioxetine in the acute treatment of adults with generalised anxiety disorder

AIMS

This study aims to evaluate the efficacy and tolerability of vortioxetine 2.5-, 5- and 10-mg once-daily doses vs. placebo in the treatment of generalised anxiety disorder (GAD).

METHODS

In this 8-week, multicentre, double-blind, placebo-controlled, parallel-group, phase 3 study, patients with a primary GAD diagnosis were randomised to receive placebo (n = 157), vortioxetine 2.5 mg, vortioxetine 5 mg, vortioxetine 10 mg or duloxetine 60 mg once daily (n = 156 each). The primary end-point, mean change from baseline in Hamilton Anxiety Scale (HAM-A) total score and key secondary end-points for the 5- and 10-mg vortioxetine doses were analysed in a prespecified sequential testing procedure (all at week 8). Sexual dysfunction was evaluated using the Arizona Sexual Experiences Scale.

RESULTS

Differences from placebo in the primary efficacy end-point were not statistically significant for the vortioxetine groups. The mean difference from placebo was significant in the duloxetine arm. For all secondary efficacy end-points, results were similar among the vortioxetine groups and did not reach statistical significance. The vortioxetine 10-mg group showed separation from placebo on the Hospital Anxiety and Depression anxiety subscore (nominal p = 0.036). Duloxetine 60 mg significantly improved the primary end-point (p < 0.05 vs. placebo), validating the study. Nausea, dry mouth, diarrhoea, nasopharyngitis, headache, dizziness, somnolence, vomiting, dyspepsia, constipation and fatigue were reported in ≥ 5% of patients receiving vortioxetine. Rates of treatment-emergent sexual dysfunction (TESD) in the vortioxetine dosing groups were similar to placebo.

CONCLUSION

In this study, vortioxetine 2.5-, 5- and 10-mg once-daily doses showed no significant improvement in HAM-A total scores vs. placebo. Vortioxetine was well tolerated at all doses and was not associated with TESD.

Vortioxetine for major depressive disorder: a systematic review of the efficacy and safety profile for this newly approved antidepressant - what is the number needed to treat, number needed to harm and likelihood to be helped or harmed?

OBJECTIVE

To describe the efficacy and safety of vortioxetine for the treatment of major depressive disorder (MDD).

DATA SOURCES

The pivotal registration trials were accessed by querying http://www.ncbi.nlm.nih.gov/pubmed/, http://www.clinicaltrialsregister.eu and http://www.clinicaltrials.gov for the search terms 'vortioxetine' and 'Lu AA21004', and by obtaining posters presented at congresses. Product labelling provided additional information.

STUDY SELECTION

All available clinical reports of studies were identified.

DATA EXTRACTION

Descriptions of the principal results and calculation of number needed to treat (NNT) and number needed to harm (NNH) for relevant dichotomous outcomes were extracted from the available study reports and other sources of information.

DATA SYNTHESIS

Vortioxetine is a multi-modal antidepressant that functions as a human 5-HT3A and 5-HT7 receptor antagonist, 5-HT1B receptor partial agonist, 5-HT1A receptor agonist, and inhibitor of the serotonin transporter. The recommended dose range is 5-20 mg/day. Approval for the treatment of MDD was based on a clinical development programme that included six positive 6-8 week studies, including one study in elderly people, and one positive maintenance study in adults. In the informative short-term studies in non-elderly patients, NNT for response with vortioxetine vs. placebo was 7 (95% CI 6-9), and NNT for remission vs. placebo was 11 (95% CI 8-17). NNH for discontinuation because of an adverse event (AE) was 36 (95% CI 24-70). The most commonly encountered AEs (incidence ≥ 5% and at least twice the rate of placebo) as identified in product labelling were nausea, constipation and vomiting, with NNH values vs. placebo of 6 (95% CI 6-7), 64 (95% CI 37-240), and 28 (95% CI 23-38), respectively. Changes in weight were not clinically relevant.

CONCLUSIONS

Vortioxetine represents another option for the treatment of MDD. Vortioxetine appears to have a favourable weight-gain profile. Additional information regarding the time course of response/remission and for the commonly occurring AE of nausea would be helpful to better characterise this agent. Pending clinical trials include those examining cognitive dysfunction that can accompany MDD.

Vortioxetine dose-dependently reverses 5-HT depletion-induced deficits in spatial working and object recognition memory: a potential role for 5-HT1A receptor agonism and 5-HT3 receptor antagonism

We previously reported that the investigational multimodal antidepressant, vortioxetine, reversed 5-HT depletion-induced memory deficits while escitalopram and duloxetine did not. The present report studied the effects of vortioxetine and the potential impact of its 5-HT1A receptor agonist and 5-HT3 receptor antagonist properties on 5-HT depletion-induced memory deficits. Recognition and spatial working memory were assessed in the object recognition (OR) and Y-maze spontaneous alternation (SA) tests, respectively. 5-HT depletion was induced in female Long-Evans rats using 4-cholro-DL-phenylalanine methyl ester HCl (PCPA) and receptor occupancies were determined by ex vivo autoradiography. Rats were acutely dosed with vortioxetine, ondansetron (5-HT3 receptor antagonist) or flesinoxan (5-HT1A receptor agonist). The effects of chronic vortioxetine administration on 5-HT depletion-induced memory deficits were also assessed. 5-HT depletion reliably impaired memory performance in both the tests. Vortioxetine reversed PCPA-induced memory deficits dose-dependently with a minimal effective dose (MED) ≤0.1mg/kg (∼80% 5-HT3 receptor occupancy; OR) and ≤3.0mg/kg (5-HT1A, 5-HT1B, 5-HT3 receptor occupancy: ∼15%, 60%, 95%) in SA. Ondansetron exhibited a MED ≤3.0μg/kg (∼25% 5-HT3 receptor occupancy; OR), but was inactive in the SA test. Flesinoxan had a MED ≤1.0mg/kg (∼25% 5-HT1A receptor occupancy; SA); only 1.0mg/kg ameliorated deficits in the NOR. Chronic p.o. vortioxetine administration significantly improved memory performance in OR and occupied 95%, 66%, and 9.5% of 5-HT3, 5-HT1B, and 5-HT1A receptors, respectively. Vortioxetine's effects on SA performance may involve 5-HT1A receptor agonism, but not 5-HT3 receptor antagonism, whereas the effects on OR performance may involve 5-HT3 receptor antagonism and 5-HT1A receptor agonism.

Chronic interferon-α decreases dopamine 2 receptor binding and striatal dopamine release in association with anhedonia-like behavior in nonhuman primates

Neuroimaging studies in humans have demonstrated that inflammatory cytokines target basal ganglia function and presynaptic dopamine (DA), leading to symptoms of depression. Cytokine-treated nonhuman primates also exhibit evidence of altered DA metabolism in association with depressive-like behaviors. To further examine cytokine effects on striatal DA function, eight rhesus monkeys (four male, four female) were administered interferon (IFN)-α (20 MIU/m(2) s.c.) or saline for 4 weeks. In vivo microdialysis was used to investigate IFN-α effects on DA release in the striatum. In addition, positron emission tomography (PET) with [(11)C]raclopride was used to examine IFN-α-induced changes in DA2 receptor (D2R) binding potential before and after intravenous amphetamine administration. DA transporter binding was measured by PET using [(18)F]2β-carbomethoxy-3β-(4-chlorophenyl)-8-(2-fluoroethyl)nortropane. Anhedonia-like behavior (sucrose consumption) was assessed during saline and IFN-α administration. In vivo microdialysis demonstrated decreased release of DA after 4 weeks of IFN-α administration compared with saline. PET neuroimaging also revealed decreased DA release after 4 weeks of IFN-α as evidenced by reduced displacement of [(11)C]raclopride following amphetamine administration. In addition, 4 weeks of IFN-α was associated with decreased D2R binding but no change in the DA transporter. Sucrose consumption was reduced during IFN-α administration and was correlated with decreased DA release at 4 weeks as measured by in vivo microdialysis. Taken together, these findings indicate that chronic peripheral IFN-α exposure reduces striatal DA release in association with anhedonia-like behavior in nonhuman primates. Future studies examining the mechanisms of cytokine effects on DA release and potential therapeutic strategies to reverse these changes are warranted.

Involvement of serotonin 5-HT3 receptors in the modulation of noradrenergic transmission by serotonin reuptake inhibitors: a microdialysis study in rat brain

RATIONALE

Selective serotonin reuptake inhibitors (SSRIs), in addition to being able to enhance serotonergic neurotransmission, are able to modulate other brain systems involved in depression.

OBJECTIVES

This study evaluates the neurochemical effect of the SSRI citalopram on brain noradrenergic activity and the serotonin receptor involved in this effect.

METHODS

Dual-probe microdialysis in the locus coeruleus (LC) and prefrontal cortex (PFC) was performed in freely awake rats.

RESULTS

Systemic citalopram (10 mg/kg, i.p.) increased noradrenaline (NA) in the LC (E max = 141 ± 13%) and simultaneously decreased NA in the PFC (Emax = -46 ± 7%). In the local presence into the LC of the α2-adrenoceptor antagonist RS79948 (1 μM), systemic citalopram increased NA in the LC (Emax = 157 ± 25%) and PFC (Emax = 175 ± 24%). Local citalopram (0.1-100 μM) into the LC induced NA increase in the LC (Emax = 210 ± 25%) and decrease in the PFC (Emax = -38 ± 9%). Local LC citalopram effect was abolished by LC presence of the 5-HT3 receptor antagonist MDL72222 (1 μM) but not the 5-HT1/2 receptor antagonist methiothepin (1 μM). Systemic citalopram in the LC presence of MDL72222 did not modify NA in the LC but increased NA in the PFC (Emax = 158 ± 26%). Local citalopram into the PFC enhanced NA (Emax = 376 ± 18%) in the area, which was prevented by MDL72222.

CONCLUSIONS

The SSRI citalopram modulates central noradrenergic neurotransmission by activation, through endogenous serotonin, of 5-HT3 receptors expressed in the somatodendritic (LC) and terminal (PFC) areas, which subsequently promote an enhancement of local NA. Therefore, 5-HT3 receptors and somatodendritic α2-adrenoceptors in the LC play an important role in the global effect of SSRIs.

Monoamine neurocircuitry in depression and strategies for new treatments

Extensive studies showed that monoaminergic neurotransmission that involves serotonin (5-HT), norepinephrine (NE) and dopamine (DA) exerts major influence on brain circuits concerned by the regulation of mood, reactivity to psychological stress, self-control, motivation, drive, and cognitive performance. Antidepressants targeting monoamines directly affect the functional tone of these circuits, notably in limbic and frontocortical areas, and evidence has been provided that this action plays a key role in their therapeutic efficacy. Indeed, at least some of functional changes detected by functional magnetic resonance imaging in emotion- and cognitive-related circuits such as the one involving limbic-cortical-striatal-pallidal-thalamic connections in depressed patients can be reversed by monoamine-targeted antidepressants. However, antidepressants acting selectively on only one monoamine, such as selective inhibitors of 5-HT or NE reuptake, alleviate depression symptoms in a limited percentage of patients, and are poorly effective to prevent recurrence. Thorough investigations for the last 30 years allowed the demonstration of the existence of functional interactions between 5-HT, NE and DA systems, and the identification of the specific receptors involved. In particular, 5-HT systems were shown to exert negative influence on NE and DA systems through 5-HT2A and 5-HT2C receptor- mediated mechanisms, respectively. On the other hand, complex positive and negative influences of NE system on 5-HT neurotransmission are mediated through α1- and α2-adrenergic receptors, respectively. These data provided a rationale for the design of new, multimodal, therapeutic strategies involving drugs acting not only at the "historical" targets such as the 5-HT and/or the NE transporter, but also at other molecular targets to improve their efficacy and their tolerability.

The rapid recovery of 5-HT cell firing induced by the antidepressant vortioxetine involves 5-HT(3) receptor antagonism

The therapeutic effect of current antidepressant drugs appears after several weeks of treatment and a significant number of patients do not respond to treatment. Here, we report the effects of the multi-modal antidepressant vortioxetine (Lu AA21004), a 5-HT(3) and 5-HT(7) receptor antagonist, 5-HT(1B) receptor partial agonist, 5-HT(1A) receptor agonist and 5-HT transporter (SERT) inhibitor, on rat 5-HT neurotransmission. Using in vivo electrophysiological recordings in the dorsal raphe nucleus of anaesthetized rats, we assessed the acute and subchronic effects of vortioxetine and/or the selective 5-HT(3) receptor agonist, SR57227 or the selective 5-HT(1A) receptor agonist flesinoxan, on 5-HT neuronal firing activity. Using ex-vivo autoradiography, we correlated SERT occupancy and presumed 5-HT firing activity. The selective serotonin reuptake inhibitor, fluoxetine, was used as comparator. Importantly, the recovery of 5-HT neuronal firing was achieved after 1 d with vortioxetine and 14 d with fluoxetine. SR57227 delayed this recovery. In contrast, vortioxetine failed to alter the reducing action of 3 d treatment of flesinoxan. Acute dosing of vortioxetine inhibited neuronal firing activity more potently than fluoxetine. SR57227 prevented the suppressant effect of vortioxetine, but not of fluoxetine. In contrast, flesinoxan failed to modify the suppressant effect of vortioxetine acutely administered. Differently to fluoxetine, vortioxetine suppressed neuronal firing without saturating occupancy at the SERT. Vortioxetine produced a markedly faster recovery of 5-HT neuronal firing than fluoxetine. This is at least partly due to 5-HT(3) receptor antagonism of vortioxetine in association with its reduced SERT occupancy.

Antidepressant and anxiolytic potential of the multimodal antidepressant vortioxetine (Lu AA21004) assessed by behavioural and neurogenesis outcomes in mice

Vortioxetine (Lu AA21004) is an investigational novel antidepressant with multimodal activity that functions as a 5-HT3, 5-HT7 and 5-HT(1D) receptor antagonist, 5-HT(1B) receptor partial agonist, 5-HT(1A) receptor agonist and inhibitor of the 5-HT transporter in vitro. Here we explore its anxiolytic and antidepressant potential in adult mice. Vortioxetine was assessed in BalB/cJ@RJ mice using the open-field and forced-swim tests (acute: p.o. 1 h, repeated: daily p.o. 21 days), and in 129S6/SvEvTac mice using the novelty suppressed feeding paradigm (acute: p.o. 1 h, sustained: daily p.o. 14 or 21 days). Fluoxetine and diazepam were controls. Acute and repeated dosing of vortioxetine produced more pronounced anxiolytic- and antidepressant-like activities than fluoxetine. Vortioxetine significantly increased cell proliferation and cell survival and stimulated maturation of immature granule cells in the subgranular zone of the dentate gyrus of the hippocampus after 21 days of treatment. After 14 days, a high dose of vortioxetine increased dendritic length and the number of dendrite intersections, suggesting that vortioxetine accelerates the maturation of immature neurons. Vortioxetine displays an antidepressant and anxiolytic profile following repeated administration associated with increased neurogenesis at several stages. Vortioxetine effects were observed at low levels of 5-HT transporter occupancy, suggesting an alternative mechanism of action to 5-HT reuptake inhibition.

Vortioxetine (Lu AA21004), a novel multimodal antidepressant, enhances memory in rats

The serotonergic system plays an important role in cognitive functions via various 5-HT receptors. Vortioxetine (Lu AA21004) in development as a novel multimodal antidepressant is a 5-HT3, 5-HT7 and 5-HT1D receptor antagonist, a 5-HT1B receptor partial agonist, a 5-HT1A receptor agonist and a 5-HT transporter (5-HTT) inhibitor in vitro. Preclinical studies suggest that 5-HT3 and 5-HT7 receptor antagonism as well as 5-HT1A receptor agonism may have a positive impact on cognitive functions including memory. Thus vortioxetine may potentially enhance memory. We investigated preclinical effects of vortioxetine (1-10mg/kg administered subcutaneously [s.c.]) on memory in behavioral tests, and on cortical neurotransmitter levels considered important in rat memory function. Contextual fear conditioning and novel object recognition tests were applied to assess memory in rats. Microdialysis studies were conducted to measure extracellular neurotransmitter levels in the rat medial prefrontal cortex. Vortioxetine administered 1h before or immediately after acquisition of contextual fear conditioning led to an increase in freezing time during the retention test. This mnemonic effect was not related to changes in pain sensitivity as measured in the hotplate test. Rats treated with vortioxetine 1h before training spent more time exploring the novel object in the novel object recognition test. In microdialysis studies of the rat medial prefrontal cortex, vortioxetine increased extracellular levels of acetylcholine and histamine. In conclusion, vortioxetine enhanced contextual and episodic memory in rat behavioral models. Further demonstration of its potential effect on memory functions in clinical settings is warranted.

A rodent model of premenstrual dysphoria: progesterone withdrawal induces depression-like behavior that is differentially sensitive to classes of antidepressants

Premenstrual dysphoric disorder (PMDD) is characterized by a range of physical and affective symptoms including anxiety, irritability, anhedonia, social withdrawal and depression. We demonstrate robust and reproducible depression-like behavior during progesterone withdrawal (PWD) protocols with different methodological variables. Comparable immobility in the forced swim test was evident with different routes of administration (i.e. injections vs. implants), with and without exogenous estrogens in addition to progesterone, and in both single and multiple withdrawal paradigms. Furthermore, withdrawal from physiological doses of progesterone resulted in modest social withdrawal in the social preference test and anhedonia in the saccharin preference test without altering general activity levels or total liquid consumption. However, progesterone withdrawal did not alter serotonin levels in the cortex or hippocampus. Furthermore tryptophan depletion did not augment immobility during PWD. Neither fluoxetine nor duloxetine reduced depression-like behavior during PWD in the forced swim test. In contrast, the tricyclic antidepressant, amitriptyline, was effective in reducing the immobility in forced swim test. These data demonstrate that progesterone withdrawal is a reproducible model of PMDD in several critical behavioral domains. Furthermore, these data do not support alterations in serotonin levels in the etiology of hormonally induced depression.