Carlos A. Zarate, M.D. - US grants

Sleep deprivation is one of the only interventions that have consistently been demonstrated to produce rapid antidepressant effects. The mechanisms by which sleep deprivation brings about rapid antidepressant effects have not been elucidated. It is noteworthy; however, that recent genomic and proteomic studies have shown that acute sleep deprivation rapidly brings about an upregulation of several mediators of neuronal plasticity, most notably CREB and BDNF. Intriguingly, these very same molecules are upregulated by chronic antidepressants, and may underlie the delayed therapeutic effects of most antidepressants. Additional investigation of the regulation of CREB and BDNF by sleep deprivation has revealed that these changes are critically dependent upon the activation of the noradrenergic system. This is particularly noteworthy, since the locus coeruleus noradrenergic projection is quiescent only during rapid eye movement sleep (REM), when the target tissues display their greatest sensitivity; indeed, the temporal dissociation between the firing of the locus coeruleus noradrenergic neurons, and the sensitivity of its postsynaptic targets in the cortex may have considerable relevance for the antidepressant effects of sleep deprivation. In this context, biological rhythms have the capacity to temporally dissociate biochemical processes, and imposing a temporal coincidence on normally dissociated events can have striking and unexpected effects. Thus, it is our hypothesis that activating the normally quiescent noradrenergic system during REM sleep (i.e. when its postsynaptic target system displays its greatest sensitivity) will robustly upregulate CREB and BDNF, thereby bringing about a rapid antidepressant effect. We propose to activate the noradrenergic system during REM sleep by infusing an alpha-2 antagonist, yohimbine. Since it is our hypothesis that activating the noradrenergic system during REM sleep will bring about an antidepressant effect by a similar mechanism as sleep deprivation, we will enrich our sample with sleep deprivation responders in this pilot study.[unreadable] Patients, ages 18 to 60 with a diagnosis of major depressive disorder, currently depressed without psychotic features will be recruited into this study. This experimental proof-of-concept study has two Study Phases. Study Phase I consists of total sleep deprivation. Responders to total sleep deprivation who subsequently relapse will enter Study Phase II. Study Phase II is a double-blind crossover administration of either intravenous yohimbine or saline solution during REM sleep. [unreadable] The specific aim of this study is to assess the efficacy of a single dose of intravenous yohimbine hydrochloride (0.125 mg/kg given over 3 minutes) compared with placebo in improving overall depressive symptomatology when administered during REM sleep. [unreadable] Our primary hypothesis is that the intravenous use of an antagonist in patients with major depression during REM sleep will activate the LC and thus increase noradrenergic activity during a time when the locus coeruleus is normally quiescent- namely REM sleep. If the hypothesis that the timing of the activation of the noradrenergic system is crucial in the antidepressant effect of sleep deprivation is correct then an acute antidepressant effect should be observed in patients despite minimal to no disruption of sleep.[unreadable] This project is now highly integrated with project MH002857-04 Glutamatergic Modulators for Rapid & Sustained Antidepressant Effect where we found that a glutamatergic modulator led to rapid antidepressant effects in 4 hours instead of 6 weeks as occurs with standard antidepressants. The present study is anticipated to be completed in the next year. One of the aims of this study is to examine brain derived neurotrophic factor (BDNF) which has been implicated in the mechanism of action of existing antidepressant but the change in BDNF often takes several weeks to increase which coincides with the therapeutic onset effect. The current project has collected BDNF plasma levels in patients with major depression to determine whether these could acutely change in a matter of hours instead of weeks with sleep deprivation; if an increase in BDNF does indeed rapidly increase with sleep deprivation then in theory that would result in a rapid onset of antidepressant action. While we have not yet analyzed BDNF levels in patients with major depression undergoing sleep deprivation, the other study which this is closely linked to (see above MH002857-04) did not find changes in BDNF in individuals with major depression within 4 hours of an infusion with an NMDA antagonist (ketamine) even though these patients responded to ketamine in that time frame. This suggests that developing compounds that increase BDNF rapidly may not be a feasible strategy to obtain rapid antidepressant response. BDNF might be more relevant for maintenance of antidepressant response. As we complete this study in the next 1-2 years, we will however, be able to determine whether the rapid-onset of antidepressant action with sleep deprivation is linked or not with BDNF.

Preclinical and clinical studies suggest that drugs that modulate the glutamatergic system might result in therapeutic effects in patients with mood disorders. Antidepressants have been demonstrated to have delayed indirect effects on this system. Lamotrigine, an inhibitor of glutamate release, is an approved treatment for bipolar disorder. Our group found in two separate open studies that the glutamate modulating agent riluzole (inhibitor of glutamate release, and enhancer of AMPA trafficking and glutamate reuptake) was effective in treatment-resistant unipolar and bipolar depression. Collectively, these data suggest that the glutamatergic system may play a role in the pathophysiology and treatment of depression, and that agents which more directly reduce glutamatergic neurotransmission, may represent a novel class of antidepressants. The efficacy of riluzole in treatment-resistant bipolar depression is currently being tested in a double-blind placebo-controlled study. Participants, ages 18 to 70 years with bipolar disorder currently in a major depressive episode are actively being recruited and randomized to double-blind, treated to receive either riluzole (50-200 mg/day) or placebo for a period of 8 weeks. Acute efficacy will be determined by demonstrating a greater response rate in the Montgomery-Asberg Depression Rating scale. This controlled study is still ongoing and actively recruiting subjects. The study blind has not been broken.

Despite the availability of a wide range of antidepressant drugs, 30% to 40% of patients with major depression fail to respond to first-line antidepressant (e.g., selective serotonin reuptake inhibitors SSRIs) treatment, despite adequate dosage, duration, and compliance. Furthermore, these medications may take weeks to months to achieve their full effects, and in the meantime patients continue to suffer from their symptoms and continue to be at risk of self-harm as well as harm to their personal and professional lives. Thus, there is a clear need to develop novel and improved therapeutics for treatment-resistant major depression that are more effective and have a rapid onset of action. Preclinical and clinical studies suggest that antidepressants with a combined mechanism of action (e.g., combination of a selective serotonin-reuptake inhibitor (SSRI) and a norepinephrine reuptake inhibitor) may be more effective than either agent alone in achieving remission (Nelson et al 2004). Thus, it stands to reason that other combinations of antidepressants with other mechanisms of action when combined may have a synergistic effect that is superior to an antidepressant with a single mechanism of action. Preclinical and clinical studies suggest that the dopaminergic system may play a major role in the pathophysiology of depression. Preclinical studies suggest synergistic antidepressant effects with the combination of a SSRI and a selective D3 receptor agonist in animal models of depression. Similarly, preliminary clinical studies suggest synergism with combination treatment that affects the serotonin and dopamine systems. Together, these data suggest that treatments which affect the serotonin and dopamine systems will be more effective than agents which use a single mechanism. We propose to compare the combination of a selective dopaminergic agonist and a SSRI in patients with treatment-resistant major depression. To our knowledge, this will be the only controlled double-blind study to date that will examine the efficacy of a serotonin and dopamine combination given from the start of treatment.[unreadable] Patients, ages 18 years or older, with a diagnosis of major depression (without psychotic features), will be randomized to the combination of a selective dopaminergic receptor agonist and a SSRI or either drug alone for a period of 6 weeks. Acute efficacy will be determined by demonstrating a greater remission rate using specified criteria. Approximately 85 patients with acute major depression will be enrolled in the study.[unreadable] [unreadable] Other aims of this study are to examine correlates of antidepressant response to clinical (e.g., family history), and imaging (magnetic resonance imaging/spectroscopy) correlates.

Clinical Studies:The role of cholinergic system in mood disorders has been highlighted recently through our demonstration that blocking cholinergic muscarinic activity with scopolamine produces rapid antidepressant effects. Our early studies identified an antidepressant effect of scopolamine in both MDD and BD patients. Significant (p< 0.001) clinical improvement occurred following a single infusion of scopolamine. Over the course of the clinical trial, 70% of patients experience a full response (50% reduction in symptoms) and over 50% experience remission of symptoms.A replication of our original finding was published in an independent MDD sample of patients. Moreover, we observed that while men and women show significant clinical improvement following scopolamine, women show a larger response than do men (p< 0.01). Recently, we conducted a pharmacokinetic study to identify an alternative route of scopolamine administration. The NIH pharmacy developed a nasal spray formulation, and over the past year we completed the collection of pharmacokinetic data to identify the nasal spray dose that most closely approximates the area-under-the-curve obtained with the i.v. administration. These samples currently are being processed by our collaborator, Irving Wainer, PhD. Clinical trials utilizing this route of administration potentially will begin within the next year. Cognitive and Imaging Studies: Behavioral and cognitive features of depression are associated primarily with the processing of affective information. A consistently reported finding is a mood congruent processing bias, which is defined as a tendency to show a bias for processing negative as compared to positive or neutral information. The mood congruent processing bias observed in MDD can be characterized within the framework of cholinergic system and stimulus processing mechanisms. The biased processing of negative or sad information is consistent with over-active cholinergic function in depression resulting in the over-representation of negative information. We would hypothesize that competition among stimuli in the environment engages cholinergic system, and the overactive system alters the bias preferentially towards negative stimuli in MDD. We are utilizing functional brain imaging methods to elucidate the role of the cholinergic system in stimulus processing biases. We characterized behaviorally a stimulus processing bias associated with a selective attention task where face and house stimuli are presented simultaneously. Faster reaction time when attending to faces (vs houses) reflects a stimulus process bias towards faces. Scopolamine selectively increased reaction time when attending to face stimuli with no change when attending to houses, reflecting a stimulus specific shift in the processing bias. The brain regions in visual processing areas which show a bias towards faces (larger response to faces than to houses) during placebo, reduce the bias during scopolamine, a result that complements the behavioral finding. In brain regions that show a bias for processing houses during placebo, no change is observed following scopolamine. Acetylcholine also influences working memory (WM) function through stimulus processing mechanisms and particularly is critical to the encoding of information through stimulus processing mechanisms. We evaluated the influence of blocking cholinergic muscarinic activity on neural responses during WM encoding as the attended stimulus feature was modulated in a fMRI study. During the task a picture of a face was shown (encoding) followed by a delay component (maintenance) then another picture of a face (test/retrieval). Healthy participants were instructed to match the test stimulus to either the identity or the emotional expression of the encoded face. Neural activity associated with encoding was estimated for the emotion and identity task conditions. Blocking cholinergic muscarinic receptors preferentially reduced BOLD response during encoding selectively when attending to the emotional stimulus content, with no change when attending to identity. This finding suggests that the more salient stimulus feature (i.e. emotion) is more susceptible to cholinergic modulation. Biomarker of Treatment Response Clinical Markers of Treatment Response. We evaluated the potential for baseline clinical ratings to predict treatment response to scopolamine. We conducted a discriminant function analysis to determine if a linear combination of self-report mood-ratings could discriminate treatment responders from non-responders. Moreover, we used a validation procedure to determine if we could predict at baseline whether individual patients would be a responder or a non-responder following scopolamine treatment. The disciminant function identified a set of 4 or 5 clinical ratings that, when combined into a linear function, classified 86% of unipolar patients as responders or non-responders (p= 0.002); the discriminant function scores differed significantly between the responders and non-responders (p< 0.001). The validation analysis was able to correctly predict classification in over 70% of MDD patients. Similarly, the discriminant function classified 88% of BP patients, and the discriminant fuction scores differed significantly between the responders and non-responders (p< 0.001). The validation analysis in the BP group was able to correctly predict classification in over 85% of the patients. These results indicate that baseline self-report mood-ratings obtained prior to treatment can predict response outcome to scopolamine.We also are considering potential clinical or patient variables that might contribute to the identification of patients who will response to scopolamine treatment. Previously we demonstrated that gender influenced treatment outcome and we currently are evaluating other variables including family history of mood disorders; family history of alcohol abuse; comorbid anxiety disorder etc. These analyses are underway. Functional Imaging Markers of Treatment Response. We evaluated whether the functional brain response during WM may predict the antidepressant response to scopolamine. A group of MDD patients participated in a fMRI study using the WM task described above. Imaging data were obtained at baseline and following scopolamine. Neural activity (at baseline) associated with each separate task component was correlated with the magnitude of treatment response at study end. Correlations (p< 0.01) were seen in visual processing areas for the encoding and retrieval components of WM, selectively during the emotion task with no correlation in the identity task. Following treatment with scopolamine, changes in neural response in these same brain regions also correlated with the magnitude of response. We show that baseline levels of neural activity in visual processing areas reflect potential for response to treatment with scopolamine. The cortical regions that show baseline predictive value for treatment response also respond to cholinergic modulation, which argues that baseline differences are cholinergically mediated. Using a selective attention task, we also conducted analyses to evaluate if a brain response index that reflects emotional processing biases also predicts treatment response. We found that neural activity at baseline (prior to treatment) in both the anterior cingulated cortex and visual processing areas (which overlap with areas identified in the working memory task) correlated with subsequent treatment response to scopolamine. Interestingly, the pattern of correlation was opposite in the anterior cingulated and in visual cortex. These findings indicate that difference in response patterns based on emotional content of information has the potential to predict subsequent response to treatment with scopolamine.

Recent preclinical and clinical studies suggest that the glutamatergic system is involved in the mechanism of action of antidepressants. We found that the non-competitive NMDA antagonist (ketamine) was effective in treatment-resistant major depression. Ketamine resulted in rapid, robust and relatively sustained antidepressant effects. Response with ketamine occurred within 2 hours and lasted approximately 1 week. The current protocol consists of 3 primary studies designed to address 3 major questions: Study 1 (Rapid improvement research in unipolar depression) OBJECTIVE: To determine whether a rapid antidepressant effect can be achieved with an antagonist at the N-methyl-D-aspartate receptor in subjects with major depression. We found robust and rapid antidepressant effects resulted from a single intravenous dose of an N-methyl-D-aspartate antagonist;onset occurred within 2 hours postinfusion and continued to remain significant for 1 week. There is now an ongoing study with subunit selective NMDA antagonists (NR2A and NR2B). Study 2 (Rapid improvement research in bipolar depression) Does the NMDA antagonist ketamine produce rapid antidepressant effects in patients with treatment-resistant bipolar depression? The efficacy component of the study is completed and the data are being analyzed. The study remains open for active recruitment as more subjects are required to complete the neurophysiological (MEG, PSG, PET substudies) in search of biomarkers of response. Study 3 (Rapid and sustained improvement research in unipolar depression) Does riluzole (an inhibitor of glutamate release) prevent relapse in patients with treatment-resistant major depression who have rapidly responded to a single intravenous dose of ketamine? Patients ages 18 to 65 years with treatment-resistant major (unipolar) depression who have rapidly responded to a single intravenous dose of ketamine are then randomized to receive in a double-blind study with either riluzole or placebo to determine if the rapid response obtained can be sustained. The study is still actively recruiting study participants. The results from this study are not yet available because the study has not yet been completed. Our primary hypotheses for these studies are: 1) rapid response (same or next day) can be achieved in patients with treatment-resistant major (unipolar) depression, 2) rapid response (same or next day) can be achieved in patients with treatment-resistant bipolar depression, and 3) rapid response (same or next day) can be sustained in patients with treatment-resistant unipolar depression. Other aims are 1) to examine the antisuicidal effects of ketamine, and 2) to examine correlates of antidepressant response to ketamine in both major depressive disorder and bipolar disorder and include: clinical (e.g., family history), imaging (positron emission tomography PET, magnetic resonance imaging/spectroscopy), electrophysiological (magnetoencephalography MEG, electroencephalography EEG), neuropsychological, and biochemical (e.g., genetics, microRNA, BDNF, metabolomics), and 3) to test other glutamatergic modulators in mood disorders that target NR2A and NR2B. Results in the past year: 1) Rapid resolution of suicidal ideation after a single infusion of an N-methyl-D-aspartate antagonist in patients with treatment-resistant major depressive disorder. Suicidal ideation is a medical emergency, especially when severe. Little research has been done on pharmacologic interventions that could address this problem. Ketamine, an N-methyl-D-asparate antagonist, has been reported to have antidepressant effects within hours. We examined the effects of a single dose of ketamine on suicidal ideation in subjects with treatment-resistant major depressive disorder (MDD). Thirty-three subjects with DSM-IV-diagnosed MDD received a single open-label infusion of ketamine (0.5 mg/kg). Suicidal ideation scores decreased significantly on the SSI as well as on the suicide subscales of other rating instruments within 40 minutes;these decreases remained significant through the first 4 hours postinfusion (P <.001). Suicidal ideation in the context of MDD improved within 40 minutes of a ketamine infusion and remained improved for up to 4 hours postinfusion. Future studies with ketamine in suicidal ideation are warranted due to the potential impact on public health. 2) Rapid antidepressant effects in treatment-resistant bipolar depression. In patients with treatment-resistant bipolar depression, robust and rapid antidepressant effects resulted from a single intravenous dose of an N-methyl-D-aspartate antagonist. 3) Acute changes in mood and sleep slow waves induced by a single infusion of an NMDA antagonist in Treatment-Resistant Major Depression We examined the possible link between slow waves, sensitive markers of sleep pressure, and NMDA channel blockade as a biomarker of response to ketamine. The effects of a single ketamine infusion followed by double-blind administration of either placebo or riluzole on sleep EEG and mood were studied in 30 patients with treatment-resistant MDD. Montgomery-sberg Depression Rating Scale (MADRS) scores decreased significantly (30%) and rapidly following ketamine infusion. Compared to baseline, SWA significantly increased during the first NREM sleep episode after ketamine infusion. Furthermore, the occurrence of high amplitude waves significantly increased during the first NREM sleep episode, consistent with a net increase in synaptic efficacy. Mood effects correlated with the effects on high amplitude slow waves, consistent with an association between behavioral changes and changes at the synaptic level. Taken together, the results suggest that strengthening of cortico-cortical connections, reflected by increased SWA and slow wave amplitude, may be the physiological mechanism underlying the rapid antidepressant effects of NMDA antagonists. 4) An investigation of Amino Acid Neurotransmitters as potential predictors of clinical improvement to ketamine in depression Dysfunction of amino acid neurotransmitter systems plays a major role in the pathophysiology of major depressive disorder (MDD). Accumulating evidence shows that the NMDA antagonist ketamine produces a rapid antidepressant response in patients with treatment-resistant MDD. We herein applied proton magnetic resonance spectroscopy (1H-MRS) to investigate whether prefrontal levels of GABA, glutamate (Glu) and the ratio Glx/Glutamate (a surrogate marker of glutamine) correlate with the decrease in depressive symptoms after a single intravenous infusion of ketamine in patients with MDD. Pretreatment Glx/Glutamate ratio in the dorsomedial/dorsal anterolateral prefrontal cortex (DM/DA-PF)was negatively correlated with clinical improvement in depressive symptoms (rs(11) = -0.572, p <0.05). Pretreatment glutamate levels in the VM-PF were positively correlated with improvement in anxiety symptoms (rs(11) = 0.569, p <0.05). The findings suggest an association between lower Glx/Glutamate ratio and greater clinical improvement by ketamine treatment. Since glutamine is mainly contained in glia, the decreased glutamine found in this study may reflect the reduction in glial cells found in the same regions in post mortem studies of MDD and suggests that glial integrity may be associated with antidepressant responsiveness to ketamine.

Project 1: Enkephalinergic compounds for major depression: There is increasing evidence that patients with anxious major depressive disorder (AMDD) have a greater depressive severity, functional impairment, increased risk of suicidality, worse social distress, higher incidence of alcohol and drug abuse, and poorer treatment response and outcome than patients with non-anxious depression. There is increasing literature of the involvement of the endogenous opioid system in major depression and its treatment. Identification of delta-opioid receptor as a possible target in the treatment of depression and anxiety began with clinical observations that a heightened anxiety state and depressive-like behaviors were consistently noted in the delta-opioid receptor knockout mouse. A number of investigators have found that selective delta-opioid receptor agonists have antidepressant-like properties in models such as the forced swim test. In a search for a selective delta-opioid receptor agonist to test in a proof-of-concept clinical study in AMDD, AZD2327 is a potent, first in class, high-affinity enkephalinergic agonist that possesses anxiolytic and antidepressant activity in animal models. AZD2327 has efficacy comparable to diazepam and imipramine in rodent models of anxiety and depression, respectively. Phase I studies have been completed and have indicated an acceptable safety profile. Male and female patients, ages 18 to 65, with a diagnosis of major depression (without psychotic features) meeting criteria for AMDD, will be randomized to double-blind treatment to receive either AZD2327 (3 mg BID) or placebo in a 2:1 ratio for a period of 4 weeks. In addition, a series of surrogate neurobiological markers will be obtained to establish whether they are capable of predicting therapeutic response. Approximately 96 patients with acute major depression will be enrolled in the study. Project 2: An investigation to determine whether levels of p11 protein in peripheral blood cells correlate with treatment response to citalopram in patients with major depressive disorder. Major depressive disorder (MDD) is a serious, debilitating, life-shortening illness that affects many persons of all ages and backgrounds. While treatments are effective for a significant portion of patients with MDD, progress in developing more effective treatments is lagging. Furthermore, with regards to existing antidepressant medications, there are yet no reliable predictors of the likelihood of remission, response or non-response with an initial trial of an antidepressant medication. Identifying factors that are likely to predict response would have the advantage of personalizing treatment to a particular individual; that is, selecting the antidepressant medication that is most likely to give the greatest probability of having a favorable outcome. The serotonin system has been implicated in the pathophysiology of depression and mechanism of action ofexisting effective antidepressant treatments. Fourteen different serotonin receptors have been identified to date. One of them, 5-HT1B, plays an important role in regulating serotonin neurotransmission. Recently, p11 (a member of the S100 family of proteins) was found to interact with 5-HT1B receptors (Svenningsson et al 2006; Svenningsson and Greengard 2007). p11 mRNA levels are markedly reduced in the forebrain in helpless H/Rouen mice and the level of p11 mRNA was down-regulated in the anterior cingulate cortex from depressed patients. p11 mRNA is distributed in an anatomical pattern that closely resembled that of 5-HT1B receptor mRNA, including cortex, hippocampus, hypothalamus and raphe nuclei. Chronic administration of the antidepressants imipramine, tranylcypromine, and citalopram significantly increase the level of p11 in cortex. Finally, we have found that chronic treatment with fluoxetine increases p11 in peripheral mononuclear cells in monkeys. We will now study whether the blood cell levels of p11 differ between healthy individuals and patients suffering from unipolar depression. Moreover, we will study whether the levels of p11 are affected by treatment with the selective serotonin reuptake inhibitor, citalopram. Complementary work will continue at other laboratories to better characterize the role of p11 in the pathophysiology of depression (e.g., animal studies, post-mortem studies). In addition, we will also acquire a battery of magnetic resonance imaging (MRI) scans in a subset of 45 more homogeneous depressed subjects, and 45 matched healthy controls at baseline and at 8 weeks. There is a growing body of evidence implicating morphometric and physiologic abnormalities, measureable by MRI, in the pathophysiology of major depressive disorder. We will assess both baseline differences between depressed subjects and healthy controls, treatment effects, and search for possible MRI markers predicting treatment response. This is an open label study which will be performed at the National Institute of Mental Health. In all, 82 adult subjects with major depressive disorder, between the ages of 18 and 65 years, will be recruited from the community. In addition, we will perform p11 measurements in blood cells from 64 healthy control subjects. Project 3: Identifying biomarkers of diagnosis, illness and treatment response. Using data from the repository protocol from studies conducted in the Mood and Anxiety Disorders (MAP) which includes genetics, neuropsychological testing, structural and brain imaging, electrophysiological studies and peripheral blood measures were are examining markers of diagnosis and treatment response. Project 4. Target validation of novel treatments in mood and anxiety disorders a. NR2B antagonist in treatment-resistant major depressive disorder b. Low-trapping NMDA channel blocker in treatment-resistant major depressive disorder.

The glutamatergic study may be important to the pathophysiology and treatment of mood disorders. Lamotrigine, an inhibitor of glutamate release, is an approved treatment for bipolar disorder. We found in two separate open studies that the glutamate modulating agent riluzole (inhibitor of glutamate release, and enhancer of AMPA trafficking and glutamate reuptake) was effective in treatment-resistant unipolar and bipolar depression. Collectively, these data suggest that the glutamatergic system may play a role in the pathophysiology and treatment of depression, and that agents which more directly reduce glutamatergic neurotransmission, may represent a novel class of antidepressants. The efficacy of riluzole in treatment-resistant bipolar depression is currently being tested in a double-blind placebo-controlled study. We are also testing the efficacy of riluzole in a 4-site study (Massachusetts General Hospital, Baylor College, Yale University and NIMH) as an add-on treatment in treatment-resistant depression. Acute efficacy will be determined by demonstrating a greater response rate in the Montgomery-Asberg Depression Rating scale. This controlled study is still ongoing and actively recruiting subjects. The study blind has not been broken. Results of the add-on riluzole study in treatment-resistant unipolar depression should be completed in 2-3 years.

Our research suggests that the glutamatergic system is involved in the mechanism of action of antidepressants. We found that the non-competitive NMDA antagonist (ketamine) resulted in rapid, robust and relatively sustained antidepressant and antisuicidal effects. Response with ketamine occurred within 2 hours and lasted approximately 1 week. Comparable response rates with existing treatments occur at 6-8 weeks instead of hours. The current protocol consists of studies designed to address 3 major questions: Study 1: (Biomarkers of rapid response in major depressive disorder). OBJECTIVE: To examine what the neural correlates are of rapid antidepressant response to the NMDA antagonist ketamine in subjects with major depressive disorder. We found robust and rapid antidepressant effects resulted from a single intravenous dose of an N-methyl-D-aspartate antagonist; onset occurred within 2 hours postinfusion and continued to remain significant for 1 week. Study 2: (Biomarkers of rapid response in bipolar depression). OBJECTIVE: To examine what the neural correlates are of rapid antidepressant response to the NMDA antagonist ketamine in subjects with major depressive disorder. We found robust and rapid antidepressant effects resulted from a single intravenous dose of an N-methyl-D-aspartate antagonist; onset occurred within 2 hours postinfusion and continued to remain significant for 1 week. Aims are 1) to examine the antisuicidal effects of ketamine, and 2) to examine correlates of antidepressant response to ketamine in both major depressive disorder and bipolar disorder and include: clinical (e.g., family history), imaging (positron emission tomography PET, magnetic resonance imaging/spectroscopy), electrophysiological (magnetoencephalography MEG, electroencephalography EEG), neuropsychological, and biochemical (e.g., genetics, microRNA, BDNF, metabolomics). Results in the past year: 1) Rapid antidepressant effects in treatment-resistant bipolar depression. We replicated our previous findings with ketamine in bipolar depression. In patients with treatment-resistant bipolar depression, robust and rapid antidepressant effects resulted from a single intravenous dose of an N-methyl-D-aspartate antagonist. In addition, we found rapid antisuicidal effects within 1 hour. 2) Sleep marker are a predictor of response to ketamine Electroencephalographic (EEG) sleep slow wave activity (SWA; EEG power between 0.6 and 4Hz) has been proposed as a marker of central synaptic plasticity. Decreased generation of sleep slow waves - a core feature of sleep in depression - indicates underlying plasticity changes in the disease. We found that Delta sleep ratio (DSR) at baseline, a measure of SWA, was positively correlated with reductions in depressive scores with ketamine treatment. 3) Genetics as a predictor of response to ketamine (rapid antidepressant effect) An animal study found that normal brain derived neurotrophic factor (BDNF) function is required for the antidepressant effects of ketamine. We should that in patients with major depressive disorder that MDD patients with the Val/Val BDNF allele were more likely to exhibit increased antidepressant responses to ketamine than BDNF Met carriers. 4) Synaptic potentiation is critical for the rapid antidepressant response to ketamine We used magnetoencephalographic recordings in 20 patients with treatment-resistant depression and found that patients with robust improvements in depressive symptoms 230 min after infusion of ketamine (responders) exhibited increased cortical excitability. Specifically, we found that stimulus-evoked somatosensory cortical responses increased after infusion with ketamine, relative to pretreatment responses in responders but not in treatment nonresponders. 5) Ketamines metabolites are important in its ressponse and side effects (patent filed) A diagnostic difference was observed in the metabolism and disposition of ketamine (bipolar depression versus major depressive disorder). Concentrations of (2S,5S;2R,5R)-HNK metabolites were related to nonresponse to ketamine in bipolar depression. Some hydroxylated metabolites of ketamine correlated with psychotic and dissociative symptoms (side effects of ketamine).

Novel targets for developing new treatments for treatment-resistant major depression are urgently needed. The glutamatergic system stands as an important to target to pursue in the developing improved treatments for mood disorders. In previous work, we found that the glutamate modulating agent riluzole (inhibitor of glutamate release, and enhancer of AMPA trafficking and glutamate reuptake) was effective in treatment-resistant unipolar and bipolar depression. These data suggest that the glutamatergic system might have a key role in the pathophysiology and treatment of depression, and that agents which modulate this neurotransmitter system, may represent a novel class of antidepressants. We studied 42 subjects (18-65) with TRD and a MADRS score of 22 received a single intravenous infusion of ketamine (0.5 mg/kg). Four to six hours post-infusion, subjects were randomized to double-blind treatment with either riluzole (100-200 mg/day; n=21) or placebo (n=21) for 4 weeks. Depressive symptoms were rated daily. A significant improvement (P<0.001) in MADRS scores from baseline was found. The effect size of improvement with ketamine was initially large and remained moderate throughout the 28-day trial. Overall, 27% of ketamine responders had not relapsed by 4 weeks following a single ketamine infusion. The average time to relapse was 13.2 days. However, the difference between the riluzole and placebo treatment groups was not significant, suggesting that the combination of riluzole with ketamine treatment did not significantly alter the course of antidepressant response to ketamine alone. We have continued to enroll subjects in the search of biomarkers of treatment response. Preliminary data indicates that subjects with a) family history of alcohol use disorders have a better antidepressant response to ketamine than subjects without a family history of alcohol use disorders, and b) subjects with anxious depression have a better antidepressant response to ketamine than subjects without anxious depression. Studies are examining genetics, ketamine metabolites, and other biomarkers that might be associated with treatment response. Identifying biomarkers of response would ultimately facilitate drug discovery and development and to individualize or personalize treatment interventions.

This Report involves work collected under protocols 01-M-0254 (NCT00024635 ); 08-M-0196 (NCT00759395); 08-M-0150 (NCT00697268); 14-M-0085 (NCT02122562); 07-M-0021 (NCT00397111); 14-M-0041 (NCT02049385); and 07-M-0152 (NCT00472576), 09-M-N230; 15-M-0151 (NCT 02484456), 15-M-0188 (NCT02543983). Results this past year: 1. PET radioligand binding to translocator protein (TSPO) is increased in unmedicated depressed subjects. Inflammation is associated with major depressive disorder (MDD). Translocator protein 18 kDa (TSPO), a putative biomarker of neuroinflammation, is quantified using positron emission tomography (PET) and 11C-PBR28, a TSPO tracer. We sought to (1) investigate TSPO binding in MDD subjects currently experiencing a major depressive episode, (2) investigate the effects of antidepressants on TSPO binding, and (3) determine the relationship of peripheral and central inflammatory markers to cerebral TSPO binding. Twenty-eight depressed MDD subjects (unmedicated (n=12) or medicated (n=16)) and 20 healthy controls (HC) underwent PET imaging using 11C-PBR28. TSPO binding was higher in MDD versus HC in the subgenual prefrontal cortex (sgPFC) and anterior cingulate cortex (ACC). Unmedicated MDD subjects had the highest level of TSPO binding, followed by medicated MDD subjects, who did not differ from HC. TSPO binding correlated with interleukin-5 in cerebrospinal fluid but with no other central inflammatory markers. In conclusion, this study found a trend towards increased TSPO binding in the brains of MDD subjects, and post hoc analysis extended these findings by demonstrating that this abnormality is significant in unmedicated (but not medicated) MDD subjects. 2. Clinical Trial of the Potassium Channel Activator Diazoxide for Major Depressive Disorder Halted Due to Intolerability. Some glutamatergic modulators have demonstrated rapid and relatively sustained antidepressant properties in patients with major depressive disorder. Because the potassium channel activator diazoxide increases glutamate uptake via potassium channel activation, we hypothesized that it might exert antidepressant effects by increasing the removal of glutamate from the synaptic cleft, thereby reducing excessive glutamate transmission. This randomized, double-blind, placebo-controlled, crossover, single-site inpatient clinical study was conducted at the National Institute of Mental Health to assess the efficacy and safety of a 3-week course of diazoxide (200-400 mg daily, twice a day) versus a 3-week course of placebo in 6 participants with treatment-refractory major depressive disorder. The study was halted due to adverse effects (e.g., edema). Although the results are negative, they are an important addition to the literature in this rapidly changing field. 3. Parsing the heterogeneity of depression: An exploratory factor analysis across commonly used depression rating scales. Due to the heterogeneity of depressive symptoms-which can include depressed mood, anhedonia, negative cognitive biases, and altered activity levels-researchers often use a combination of depression rating scales to assess symptoms. This study sought to identify unidimensional constructs measured across rating scales for depression and to evaluate these constructs across clinical trials of a rapid-acting antidepressant (ketamine). Exploratory factor analysis (EFA) was conducted on baseline ratings from the Beck Depression Inventory, the Hamilton Depression Rating Scale, the Montgomery-Asberg Depression Rating Scale, and the Snaith-Hamilton Pleasure Rating Scale. Inpatients with major depressive disorder (n=76) or bipolar depression (n=43) were participating in clinical ketamine trials. The trajectories of the resulting unidimensional scores were evaluated in 41 subjects with bipolar depression who participated in clinical ketamine trials. The best solution, which exhibited excellent fit to the data, comprised eight factors: Depressed Mood, Tension, Negative Cognition, Impaired Sleep, Suicidal Thoughts, Reduced Appetite, Anhedonia, and Amotivation. Various response patterns were observed across the clinical trial data, both in treatment effect (ketamine versus placebo) and in degree of placebo response, suggesting that use of these unidimensional constructs may reveal patterns not observed with traditional scoring of individual instruments. The empirical identification of unidimensional constructs creates more refined scores that may elucidate the connection between specific symptoms and underlying pathophysiology. 4. Features of dissociation differentially predict antidepressant response to ketamine in treatment-resistant depression. Ketamine induces rapid and robust antidepressant effects, and many patients also describe dissociation, which is associated with antidepressant response. This follow-up study investigated whether antidepressant efficacy is uniquely related to dissociative symptom clusters. Treatment-resistant patients with major depressive disorder (MDD) or bipolar disorder (BD) (n=126) drawn from three studies received a single subanesthetic (0.5mg/kg) ketamine infusion. Dissociative effects were measured using the Clinician-Administered Dissociative States Scale (CADSS). Antidepressant response was measured using the Hamilton Depression Rating Scale (HAM-D). Across all studies and timepoints, the depersonalization subscale was positively related to HAM-D percent change. A significant effect of derealization on HAM-D percent change was observed at one timepoint (Day 7) in one study. The amnesia subscale was unrelated to HAM-D percent change. In conclusion, from a psychometric perspective, researchers may elect to administer only the CADSS depersonalization subscale, given that it was most closely related to antidepressant response. From a neurobiological perspective, mechanistic similarities may exist between ketamine-induced depersonalization and antidepressant response, although off-target effects cannot be excluded.

Our results indicate that the glutamatergic system is involved in the mechanism of action of rapid antidepressant response. In addition, this system may be a feasible target for developing treatments that have rapid and robust efficacy in individuals who have treatment-resistant depression and suicidal thoughts. We found that the glutamatergic modulator ketamine resulted in rapid, robust and relatively sustained antidepressant, antisuicidal, and antianhedonic effects. Response with ketamine occurred within 2 hours and lasted approximately 1 week. Comparable response rates with standard of care treatments occur at 6-8 weeks instead of hours. Study: (Biomarkers of rapid response in major depressive disorder): protocols 04-M-0222 (NCT00088699) and 17-M-0060 (NCT03065335). OBJECTIVE: To identify the neural correlates of rapid antidepressant response to the NMDA antagonist ketamine in subjects with major depressive disorder. We found robust and rapid antidepressant effects resulted from a single intravenous dose of an N-methyl-D-aspartate antagonist (ketamine); onset occurred within 2 hours post-infusion and continued to remain significant for 1 week. Aims are 1) to examine the antisuicidal effects of ketamine, and 2) to examine correlates of antidepressant response to ketamine in both major depressive disorder and bipolar disorder and include these data/outcome measures: clinical (e.g., family history), imaging (magnetic resonance imaging/spectroscopy), electrophysiological (magnetoencephalography MEG, electroencephalography EEG), neuropsychological, and biochemical (e.g., genetics, microRNA, BDNF, metabolomics), 3) To demonstrate more robust neuropharmacodynamic effects measured by neuropharmacodynamic imaging (fMRI+EEG and MEG) of ketamine 0.5 mg/kg as compared to placebo administered over 40 minutes. Secondary Outcome Measures: To determine if increases in synaptic plasticity, using electrophysiological measures in response to TMS and in association with sleep (i.e. slow wave sleep EEG activity) are associated with better antidepressant response to 0.5 mg/kg Time Frame: baseline and post-drug To demonstrate enhanced efficacy, as measured by the MADRS, of IV ketamine 0.5 mg/kg in participants with MDD using a psychophysiological technique (i.e. NPU-threat test). Time Frame: baseline and post-drug To identify baseline peripheral measures associated with response to the administration of ketamine 0.5 mg/kg, as potential biomarkers of acute (24 hour) treatment response. Time Frame: baseline and post-drug Results in the past year: 1. Ketamine produces rapid, robust, and fairly sustained antisuicidal ideation effects. Our past work, found that ketamine rapidly reduced suicidal thoughts, with effects lasting up to one week in patients across a range of depressive and non-depressive diagnoses. Suicide is a public health crisis with limited treatment options. We conducted a systematic review and individual participant data meta-analysis examining the effects of a single dose of ketamine on suicidal ideation. We found that ketamine rapidly (within 1 day) reduced suicidal ideation significantly. Effect sizes were moderate to large at all time points after dosing. We conclude that ketamine rapidly reduced suicidal thoughts, within 1 day and for up to 1 week in depressed patients with suicidal ideation. Ketamine's effects on suicidal ideation were partially independent of its effects on mood. 2. Default Mode Connectivity in Major Depressive Disorder After Ketamine Administration. The symptoms of major depressive disorder (MDD) are rapidly alleviated by administration of a single dose of the glutamatergic modulator ketamine. However, few studies have investigated the potential sustained neural effects of this agent beyond immediate infusion. This study used functional magnetic resonance imaging to examine the effect of a single ketamine infusion on the resting state default mode network (DMN) at 2 and 10 days after a single ketamine infusion in unmedicated subjects with MDD as well as healthy control subjects (HCs). Data were from a double-blind, placebo-controlled crossover study of 58 participants who received an intravenous infusion of either ketamine hydrochloride (0.5 mg/kg) or placebo on 2 separate test days spaced 2 weeks apart. Eight minutes of functional magnetic resonance imaging resting state data was acquired at baseline and at about 2 and 10 days after both infusions. In subjects with MDD, connectivity between the insula and the DMN was normalized compared with HCs 2 days postketamine infusion. Group-specific connectivity differences in drug response were observed, most notably in the insula in subjects with MDD and in the thalamus in HCs. In conclusion, connectivity changes in the insula in subjects with MDD suggest that ketamine may normalize the interaction between the DMN and salience networks, supporting the triple network dysfunction model of MDD. 3. Glutamatergic Signaling Drives Ketamine-Mediated Response in Depression. Modulating glutamatergic transmission may be critical to effectively treating depression, though the mechanisms by which this occurs are not fully understood. This double-blind, crossover, placebo-controlled study analyzed data from 18 drug-free MDD subjects and 18 heathy controls who received a single intravenous infusion of ketamine hydrochloride (0.5 mg/kg) as well as an intravenous saline placebo. Magnetoencephalographic (MEG) recordings were collected prior to the first infusion and six to nine hours after both ketamine and placebo infusions. During scanning, participants passively received tactile stimulation to the right index finger. Both MDD and healthy subjects showed ketamine-mediated NMDA-blockade sensitization, with MDD subjects showing enhanced NMDA connectivity estimates in backward connections, and controls showing enhanced NMDA connectivity estimates in forward connections in our model. Within our MDD subject group, ketamine efficacy-as measured by improved mood ratings-correlated with reduced NMDA and AMPA connectivity estimates in discrete extrinsic connections within the somatosensory cortical network. In conclusion, these findings suggest that AMPA- and NMDA-mediated glutamatergic signaling play a key role in antidepressant response to ketamine and, further, that DCM is a powerful tool for modeling AMPA- and NMDA-mediated connectivity in vivo. 4. 7T 1H-MRS in major depressive disorder: a Ketamine Treatment Study. Proton magnetic resonance spectroscopy (1H-MRS) is the only non-invasive method able to directly measure glutamate levels in vivo; in particular, glutamate and glutamine metabolite concentrations are separable by 1H-MRS at 7T. This double-blind, placebo-controlled, crossover study that included 1H-MRS scans at baseline and at 24h post ketamine and post-placebo infusions sought to determine glutamate levels in the pregenual anterior cingulate (pgACC) of 20 medication-free MDD subjects and 17 healthy volunteers (HVs) 24h post ketamine administration, and to evaluate any other measured metabolite changes, correlates, or predictors of antidepressant response. No significant between-group differences in 1H-MRS-measured metabolites were observed at baseline. Antidepressant response was not predicted by baseline glutamate levels. Our results suggest that any infusion-induced increases in glutamate at the 24-h post ketamine time point were below the sensitivity of the current technique; that these increases may occur in different brain regions than the pgACC; or that subgroups of MDD subjects may exist that have a differential glutamate response to ketamine.