A double-blind placebo-controlled trial of minocycline on translocator protein distribution volume in treatment-resistant major depressive disorder.

Gliosis is implicated in the pathophysiology of many neuropsychiatric diseases, including treatment-resistant major depressive disorder (TRD). Translocator protein total distribution volume (TSPO VT), a brain marker mainly reflective of gliosis in disease, can be measured using positron emission tomography (PET). Minocycline reduces gliosis and translocator protein binding in rodents, but this is not established in humans. Here, the ability of oral minocycline to reduce TSPO VT was assessed in TRD. To determine whether oral minocycline, as compared to placebo, can reduce prefrontal cortex (PFC), anterior cingulate cortex (ACC), and insula TSPO VT in TRD, twenty-one TRD participants underwent two [18F]FEPPA PET scans to measure TSPO VT. These were completed before and after either oral minocycline 100 mg bid or placebo which was administered in a randomized double-blinded fashion for 8 weeks. There was no significant difference between the minocycline and placebo groups on change in TSPO VT within the PFC, ACC, and insula (repeated measures ANOVA, effect of group interaction, PFC: F1,19 = 0.28, P = 0.60; ACC: F1,19 = 0.54, P = 0.47; insula F1,19 = 1.6, P = 0.22). Oral minocycline had no significant effect on TSPO VT which suggests that this dosage is insufficient to reduce gliosis in TRD. To target gliosis in TRD either alternative therapeutics or intravenous formulations of minocycline should be investigated. These results also suggest that across neuropsychiatric diseases in humans, it should be assumed that oral minocycline will not reduce TSPO VT or gliosis unless empirically demonstrated.

Translocator Protein Distribution Volume Predicts Reduction of Symptoms During Open-Label Trial of Celecoxib in Major Depressive Disorder.

BACKGROUND: Gliosis is common among neuropsychiatric diseases, but the relationship between gliosis and response to therapeutics targeting effects of gliosis is largely unknown. Translocator protein total distribution volume (TSPO VT), measured with positron emission tomography, mainly reflects gliosis in neuropsychiatric disease. Here, the primary objective was to determine whether TSPO VT in the prefrontal cortex (PFC) and anterior cingulate cortex (ACC) predicts reduction of depressive symptoms following open-label celecoxib administration in treatment-resistant major depressive disorder. METHODS: A total of 41 subjects with treatment-resistant major depressive disorder underwent one [18F]FEPPA positron emission tomography scan to measure PFC and ACC TSPO VT. Open-label oral celecoxib (200 mg, twice daily) was administered for 8 weeks. Change in symptoms was measured with the 17-item Hamilton Depression Rating Scale (HDRS). RESULTS: Cumulative mean change in HDRS scores between 0 and 8 weeks of treatment was plotted against PFC and ACC TSPO VT, showing a significant nonlinear relationship. At low TSPO VT values, there was no reduction in HDRS scores, but as TSPO VT values increased, there was a reduction in HDRS scores that then plateaued. This was modeled with a 4-parameter sigmoidal model in which PFC and ACC TSPO VT accounted for 84% and 92% of the variance, respectively. CONCLUSIONS: Celecoxib administration in the presence of gliosis labeled by TSPO VT is associated with greater reduction of symptoms. Given the predictiveness of TSPO VT on symptom reduction, this personalized medicine approach of matching a marker of gliosis to medication targeting effects of gliosis should be applied in early development of novel therapeutics, in particular for treatment-resistant major depressive disorder.

Replicating predictive serum correlates of greater translocator protein distribution volume in brain.

Greater activation of glia, a key component of neuroinflammation, is an important process to target in neuropsychiatric illnesses. However, the magnitude of gliosis varies across cases so low-cost predictors are needed to stratify subjects for clinical trials. Here, several such blood serum measures were assessed in relation to TSPO VT, an index of translocator protein density, measured with positron emission tomography. Blood serum concentration of several products known to be synthesized by activated microglia (and to some extent astroglia) [prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2α), and tumor necrosis factor alpha (TNFα)], controlled by an index of peripheral inflammation [C-reactive protein (CRP)] and TSPO VT were measured in 3 cohorts: prefrontal cortex TSPO VT of 20 subjects with major depressive episodes (MDEs) from major depressive disorder (MDD); and 56 subjects with treatment resistant MDEs from MDD; and dorsal caudate TSPO VT of 20 subjects with obsessive-compulsive disorder. Ln(PGE2/CRP) and ln(TNFα/CRP) consistently correlated with TSPO VT (R2 = 0.36 to 0.11, p = 0.0030 to p = 0.0076). Assessment of threshold serum values to predict highly elevated TSPO VT, demonstrated that a positive predictive value (PPV) of 80% was possible while retaining 40% of participant samples and that receiver operating curves (ROC) ranged from 75 to 81%. Post-hoc selection of ln(CRP) was more predictive (R2 = 0.23 to 0.39, p = 0.0058 to p = 0.00013; ROC > 80%). Systematic assessment of selected peripheral inflammatory markers is promising for developing low cost predictors of TSPO VT. Marker thresholds with high PPV will improve subject stratification for clinical trials of glial targeting therapeutics.

Association of translocator protein total distribution volume with duration of untreated major depressive disorder: a cross-sectional study.

BACKGROUND: People with major depressive disorder frequently exhibit increasing persistence of major depressive episodes. However, evidence for neuroprogression (ie, increasing brain pathology with longer duration of illness) is scarce. Microglial activation, which is an important component of neuroinflammation, is implicated in neuroprogression. We examined the relationship of translocator protein (TSPO) total distribution volume (VT), a marker of microglial activation, with duration of untreated major depressive disorder, and with total illness duration and antidepressant exposure. METHODS: In this cross-sectional study, we recruited participants aged 18-75 years from the Toronto area and the Centre for Addiction and Mental Health (Toronto, ON, Canada). Participants either had major depressive episodes secondary to major depressive disorder or were healthy, as confirmed with a structured clinical interview and consultation with a study psychiatrist. To be enrolled, participants with major depressive episodes had to score a minimum of 17 on the 17-item Hamilton Depression Rating Scale, and had to be medication free or taking a stable dose of medication for at least 4 weeks before PET scanning. Eligible participants were non-smokers; had no history of or concurrent alcohol or substance dependence, neurological illness, autoimmune disorder, or severe medical problems; and were free from acute medical illnesses for the previous 2 weeks before PET scanning. Participants were excluded if they had used brain stimulation treatments within the 6 months before scanning, had used anti-inflammatory drugs lasting at least 1 week within the past month, were taking hormone replacement therapy, had psychotic symptoms, had bipolar disorder (type I or II) or borderline antisocial personality disorder, or were pregnant or breastfeeding. We scanned three primary grey-matter regions of interest (prefrontal cortex, anterior cingulate cortex, and insula) and 12 additional regions and subregions using 18F-FEPPA PET to measure TSPO VT. We investigated the duration of untreated major depressive disorder, and the combination of total duration of disease and duration of antidepressant treatment, as predictor variables of TSPO VT, assessing their significance. FINDINGS: Between Sept 1, 2009, and July 6, 2017, we screened 134 participants for eligibility, of whom 81 were included in the study (current major depressive episode n=51, healthy n=30). We excluded one participant with a major depressive episode from the analysis because of unreliable information about previous medication use. Duration of untreated major depressive disorder was a strong predictor of TSPO VT (p<0·0001), as were total illness duration (p=0·0021) and duration of antidepressant exposure (p=0·037). The combination of these predictors accounted for about 50% of variance in TSPO VT in the prefrontal cortex, anterior cingulate cortex, and insula. In participants who had untreated major depressive disorder for 10 years or longer, TSPO VT was 29-33% greater in the prefrontal cortex, anterior cingulate cortex, and insula than in participants who were untreated for 9 years or less. TSPO VT was also 31-39% greater in the three primary grey-matter regions of participants with long duration of untreated major depressive disorder compared with healthy participants (p=0·00047). INTERPRETATION: Microglial activation, as shown by TSPO VT, is greater in patients with chronologically advanced major depressive disorder with long periods of no antidepressant treatment than in patients with major depressive disorder with short periods of no antidepressant treatment, which is strongly suggestive of a different illness phase. Consistent with this, the yearly increase in microglial activation is no longer evident when antidepressant treatment is given. FUNDING: Canadian Institutes of Health Research and Neuroscience Catalyst Fund.

Inflammation in the Neurocircuitry of Obsessive-Compulsive Disorder.

Importance: For a small percentage of obsessive-compulsive disorder (OCD) cases exhibiting additional neuropsychiatric symptoms, it was proposed that neuroinflammation occurs in the basal ganglia as an autoimmune response to infections. However, it is possible that elevated neuroinflammation, inducible by a diverse range of mechanisms, is important throughout the cortico-striato-thalamo-cortical circuit of OCD. Identifying brain inflammation is possible with the recent advance in positron emission tomography (PET) radioligands that bind to the translocator protein (TSPO). Translocator protein density increases when microglia are activated during neuroinflammation and the TSPO distribution volume (VT) is an index of TSPO density. Objective: To determine whether TSPO VT is elevated in the dorsal caudate, orbitofrontal cortex, thalamus, ventral striatum, dorsal putamen, and anterior cingulate cortex in OCD. Design, Setting, and Participants: This case-control study was conducted at a tertiary care psychiatric hospital from May 1, 2010, to November 30, 2016. Participants with OCD (n = 20) and age-matched healthy control individuals (n = 20) underwent a fluorine F 18-labeled N-(2-(2-fluoroethoxy)benzyl)-N-(4-phenoxypyridin-3-yl)acetamide PET scan. It is a high-quality second-generation TSPO-binding PET radiotracer. All participants were drug and medication free, nonsmoking, and otherwise healthy. Main Outcomes and Measures: The TSPO VT was measured in the dorsal caudate, orbitofrontal cortex, thalamus, ventral striatum, dorsal putamen, and anterior cingulate cortex. Compulsions were assessed with the Yale-Brown Obsessive Compulsive Scale. Results: In the OCD and healthy groups, the mean (SD) ages were 27.4 (7.1) years and 27.6 (6.6) years, respectively, and 11 (55%) and 8 (40%) were women, respectively. In OCD, TSPO VT was significantly elevated in these brain regions (mean, 32%; range, 31%-36% except anterior cingulate cortex, 24%; analysis of variance, effect of diagnosis: P < .001 to P = .004). Slightly lower elevations in TSPO VT (22%-29%) were present in other gray matter regions. The Yale-Brown Obsessive Compulsive Scale measure of distress associated with preventing compulsive behaviors significantly correlated with TSPO VT in the orbitofrontal cortex (uncorrected Pearson correlation r = 0.62; P = .005). Conclusions and Relevance: To our knowledge, this is the first study demonstrating inflammation within the neurocircuitry of OCD. The regional distribution of elevated TSPO VT argues that the autoimmune/neuroinflammatory theories of OCD should extend beyond the basal ganglia to include the cortico-striato-thalamo-cortical circuit. Immunomodulatory therapies should be investigated in adult OCD, rather than solely childhood OCD, particularly in cases with prominent distress when preventing compulsions.

Role of translocator protein density, a marker of neuroinflammation, in the brain during major depressive episodes.

IMPORTANCE: The neuroinflammatory hypothesis of major depressive disorder is supported by several main findings. First, in humans and animals, activation of the immune system causes sickness behaviors that present during a major depressive episode (MDE), such as low mood, anhedonia, anorexia, and weight loss. Second, peripheral markers of inflammation are frequently reported in major depressive disorder. Third, neuroinflammatory illnesses are associated with high rates of MDEs. However, a fundamental limitation of the neuroinflammatory hypothesis is a paucity of evidence of brain inflammation during MDE. Translocator protein density measured by distribution volume (TSPO VT) is increased in activated microglia, an important aspect of neuroinflammation. OBJECTIVE: To determine whether TSPO VT is elevated in the prefrontal cortex, anterior cingulate cortex (ACC), and insula in patients with MDE secondary to major depressive disorder. DESIGN, SETTING, AND PARTICIPANTS: Case-control study in a tertiary care psychiatric hospital from May 1, 2010, through February 1, 2014. Twenty patients with MDE secondary to major depressive disorder and 20 healthy control participants underwent positron emission tomography with fluorine F 18-labeled N-(2-(2-fluoroethoxy)benzyl)-N-(4-phenoxypyridin-3-yl)acetamide ([18F]FEPPA). Patients with MDE were medication free for at least 6 weeks. All participants were otherwise healthy and nonsmokers. MAIN OUTCOMES AND MEASURES: Values of TSPO VT in the prefrontal cortex, ACC, and insula. RESULTS: In MDE, TSPO VT was significantly elevated in all brain regions examined (multivariate analysis of variance, F15,23 = 4.5 [P = .001]). The magnitude of TSPO VT elevation was 26% in the prefrontal cortex (mean [SD] TSPO VT, 12.5 [3.6] in patients with MDE and 10.0 [2.4] in controls), 32% in the ACC (mean [SD] TSPO VT, 12.3 [3.5] in patients with MDE and 9.3 [2.2] in controls), and 33% in the insula (mean [SD] TSPO VT, 12.9 [3.7] in patients with MDE and 9.7 [2.3] in controls). In MDE, greater TSPO VT in the ACC correlated with greater depression severity (r = 0.63 [P = .005]). CONCLUSIONS AND RELEVANCE: This finding provides the most compelling evidence to date of brain inflammation, and more specifically microglial activation, in MDE. This finding is important for improving treatment because it implies that therapeutics that reduce microglial activation should be promising for MDE. The correlation between higher ACC TSPO VT and the severity of MDE is consistent with the concept that neuroinflammation in specific regions may contribute to sickness behaviors that overlap with the symptoms of MDE.

Differential striatal dopamine responses following oral alcohol in individuals at varying risk for dependence.

BACKGROUND: The neurobiology of risk for alcohol use disorders (AUDs) remains poorly understood. Individual differences in vulnerability, though, have been indicated by subjective responses to alcohol ingestion and personality traits. METHODS: To investigate the relationship between these features and striatal dopamine (DA) responses to alcohol, we studied 26 healthy young social drinkers (21.3 ± 3.0 years old; 10.7 ± 8.8 drinks/wk) at varying risk for alcoholism. Each participant received 2 positron emission tomography [(11) C]raclopride scans after administration of either placebo or oral alcohol (1 ml/kg body weight of 94% alcohol, 0.75 g/kg) in a randomized and counterbalanced design. RESULTS: Subjects with high-risk subjective responses to alcohol had more family members with AUDs, greater alcohol use problems, and, in response to the alcohol challenge, significant decreases in [(11) C]raclopride binding indicative of increased extracellular DA. In contrast, low-risk subjects exhibited increases in [(11) C]raclopride binding in response to alcohol. The results were similar when risk groups were based on personality traits, although statistically less robust. CONCLUSIONS: Changes in striatal DA in response to alcohol ingestion may be a neurobiological marker of vulnerability to AUDs.

Influence of the OPRM1 A118G polymorphism on alcohol-induced euphoria, risk for alcoholism and the clinical efficacy of naltrexone.

Alcohol-use disorders are thought to be heterogeneous in etiology, pathophysiology and response to treatment. One hypothesized contributor to this variability is the common A118G polymorphism of the µ-opioid receptor gene, OPRM1. This article critically evaluates the evidence that the A118G substitution affects subjective, behavioral and neurobiological responses to alcohol and the opioid receptor antagonist, naltrexone. Although screening of patients in a clinical setting remains premature, results suggest the A118G substitution may influence one etiological pathway to alcoholism, for which naltrexone pharmacotherapy is more effective.

The effect of naltrexone on alcohol's stimulant properties and self-administration behavior in social drinkers: influence of gender and genotype.

BACKGROUND: Few pharmacological treatments for alcohol dependence are available. Moreover, the best supported treatment, naltrexone hydrochloride, appears to work for only some. METHODS: To investigate potential predictors of these differential responses, 40 social drinkers (20 women) were administered 6 days of treatment with naltrexone vs. placebo in a double-blind, counterbalanced, crossover design. At the end of each treatment period, participants received a single dose of their preferred alcoholic beverage followed by the opportunity to work for additional alcohol units using a progressive ratio (PR) breakpoint paradigm. All subjects but one were genotyped for the A118G polymorphism of the mu opioid receptor gene (OPRM1). RESULTS: Naltrexone decreased the ethanol-induced 'euphoria' to a priming dose of alcohol in two subgroups: (i) in women, and (ii) in subjects with the A118G polymorphism of the mu opioid receptor gene (OPRM1). Naltrexone did not decrease motivation to work for additional alcoholic beverages on the PR task regardless of gender or genotype. CONCLUSIONS: The results add to the evidence that naltrexone decreases positive subjective effects of alcohol, with preferential effects in distinct subgroups. Similar effects in heavier drinkers might decrease alcohol use.

Effects of repeated prenatal glucocorticoid exposure on long-term potentiation in the juvenile guinea-pig hippocampus.

Synthetic glucocorticoids (sGCs) are routinely used to treat women at risk of preterm labour to promote fetal lung maturation. There is now strong evidence that exposure to excess glucocorticoid during periods of rapid brain development has permanent consequences for endocrine function and behaviour in the offspring. Prenatal exposure to sGC alters the expression of N-methyl-D-aspartate receptor (NMDA-R) subunits in the fetal and neonatal hippocampus. Given the integral role of the NMDA-R in synaptic plasticity, we hypothesized that prenatal sGC exposure will have effects on hippocampal long-term potentiation (LTP) after birth. Further, this may occur in either the presence or absence of elevated cortisol concentrations, in vitro. Pregnant guinea-pigs were injected with betamethasone (Beta, 1 mg kg(-1)) or vehicle on gestational days (gd) 40, 41, 50, 51, 60 and 61 (term approximately 70 days), a regimen comparable to that given to pregnant women. On postnatal day 21, LTP was examined at Schaffer collateral synapses in the CA1 region of hippocampal slices prepared from juvenile animals exposed to betamethasone or vehicle, in utero. Subsequently, the acute glucocorticoid receptor (GR)- and mineralocorticoid receptor (MR)-dependent effects of cortisol (0.1-10 microM; bath applied 30 min before LTP induction) were examined. There was no effect of prenatal sGC treatment on LTP under basal conditions. The application of 10 microM cortisol depressed excitatory synaptic transmission in all treatment groups regardless of sex. Similarly, LTP was depressed by 10 microM cortisol in all groups, with the exception of Beta-exposed females, in which LTP was unaltered. Hippocampal MR and GR protein levels were increased in Beta-exposed females, but not in any other prenatal treatment group. This study reveals sex-specific effects of prenatal exposure to sGC on LTP in the presence of elevated cortisol, a situation that would occur in vivo during stress.

Glucocorticoids do not alter developmental expression of hippocampal or pituitary steroid receptor coactivator-1 and -2 in the late gestation fetal guinea pig.

Steroid receptor coactivator (SRC) proteins interact with glucocorticoid receptors in a ligand-dependent manner to enhance transcription. Although glucocorticoids are essential for normal brain maturation, little is known about the presence or regulation of SRC proteins in the developing central nervous system. In the current study we demonstrated that SRC-1 was highly expressed in the fetal limbic system (hippocampal CA3>CA1/2>CA4>dentate gyrus) at gestational d (gd) 40 (term, approximately 70 d), whereas SRC-2 was undetectable at all time points. Hippocampal SRC-1 mRNA and protein expression were reduced in male and female fetuses with advancing gestation. In contrast, SRC-1 mRNA levels increased significantly in the dentate gyrus near term. Repeated maternal injection (1 or 10 mg/kg on gd 40, 41, 50, 51, 60, and 61) with synthetic glucocorticoid had no effect on fetal limbic SRC-1 expression at gd 62 in either sex. SRC-1 and SRC-2 mRNA expression in the anterior pituitary did not change over the second half of gestation and was unaffected by prenatal exposure to synthetic glucocorticoid. In conclusion, SRC-1 expression undergoes spatial, temporal, and region-specific regulation during development, and limbic and pituitary SRC-1 and SRC-2 are not regulated by glucocorticoids in late gestation. Developmental changes in limbic SRC-1 expression probably have important consequences on steroid receptor signaling, which is known to be critical for brain maturation in late gestation.

Regulation of N-methyl-D-aspartate receptor subunit expression in the fetal guinea pig brain.

N-methyl-d-aspartate receptors (NMDARs) are critical for neuronal maturation and synaptic formation as well as for the onset of long-term potentiation, a process critical to learning and memory in postnatal life. In the current study, we demonstrated that NMDAR subunits undergo spatial, temporal, and sex-specific regulation. During development, we observed increasing NR1 and NR2A expression at the same time as levels of NR2B subunits decreased in the hippocampus and cortex in the fetal guinea pig. We have also shown that glucocorticoids can modulate fetal NMDAR subunit expression in a sex-specific fashion. This is clinically important because synthetic glucocorticoids are administered to pregnant women at risk of preterm labor. Repeated exposure to exogenous glucocorticoids caused a dose-dependent decrease in NR1 mRNA levels and increased NR2A mRNA expression in the female hippocampus at Gestational Day 62. There are significant changes in NMDAR subunit expression in late gestation. It is possible that these alter NMDA-dependent signaling at this time. Prenatal exposure to exogenous glucocorticoids modifies the trajectory of NMDAR subunit expression in females but not in males.

Developmental regulation of 5-HT1A receptor mRNA in the fetal limbic system: response to antenatal glucocorticoid.

The developmental changes in 5-HT1A receptor mRNA expression associated with advancing gestational age were examined in the fetal guinea pig hippocampus and dentate gyrus (DG) by in situ hybridization. We found that 5-HT1A receptor mRNA was present in the hippocampal CA1 subfield and dentate gyrus (DG), and was significantly (P < 0.05) elevated in the DG during the period of rapid brain growth [gestational day (gd) 50; term = 70 days]. Glucocorticoids have been shown to alter 5-HT1A receptor mRNA expression in the adult, but nothing is known about their impact on the developing fetal brain. Expression of 5-HT1A receptor mRNA in the fetal hippocampus was measured following repeated maternal administration (gd40, 41, 50, 51, 60 and 61) of synthetic glucocorticoid (dexamethasone; 1 and 10 mg/kg). Levels of 5-HT1A receptor mRNA were significantly (P < 0.005) elevated in CA1 and DG following repeated exposure to high-dose glucocorticoid (10 mg/kg) in male, but not in female fetuses. Because fetal exposure to glucocorticoids programs hypothalamo-pituitary-adrenal (HPA) function, and hippocampal serotonin is known to influence glucocorticoid receptor (GR) expression, the glucocorticoid-mediated changes in 5-HT1A receptor mRNA may play a role in the programming of HPA function.

Developmental regulation of the 5-HT7 serotonin receptor and transcription factor NGFI-A in the fetal guinea-pig limbic system: influence of GCs.

Fetal exposure to excess glucocorticoids (GCs) programs the developing hypothalamo-pituitary-adrenal (HPA) axis, and may predispose offspring to adult-onset disease. During development, serotonin (5-HT) influences transcription of hippocampal GR mRNA via the 5-HT7 receptor. The effect of 5-HT on GR involves the transcription factor NGFI-A. Given the developmental changes which we have previously reported in hippocampal GR mRNA expression, we hypothesized that (1) there are progressive developmental changes in 5-HT7 receptor and NGFI-A mRNA expression in the fetal guinea-pig limbic system, and (2) repeated exposure to synthetic GC treatment will significantly modify developmental expression of these genes. 5-HT7 receptor mRNA was highly expressed in the hippocampus and thalamus at gestational day (gd) 40 (term approximately 70 days), and significantly decreased (P < 0.05) with advancing gestation. Conversely, NGFI-A mRNA expression in the hippocampus and frontal cortex was almost undetectable at gd40, but was dramatically elevated (P < 0.05; 8-fold) near term. Changes in mRNA were refelected by NGFI-A protein levels. These changes were significantly correlated to hippocampal GR expression and fetal plasma cortisol concentrations. Synthetic GC treatment increased NGFI-A mRNA levels in CA1 and the cingulate cortex, but had no effect on 5-HT7 receptor expression. In conclusion our results suggest that (1) limbic 5-HT7 receptor expression is not directly linked to maturation of hippocampal GR in late gestation; (2) the up-regulation of NGFI-A expression near term is driven by glucocorticoid; and (3) premature exposure to synthetic glucocorticoid significantly increases NGFI-A-related transcriptional activity in the fetal limbic system.