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Psychiatric disorders are the leading cause of disability worldwide while the pathogenesis remains unclear. Genome-wide association studies (GWASs) have made great achievements in detecting disease-related genetic variants. However, functional information on the underlying biological processes is often lacking. Current reports propose the use of metabolic traits as functional intermediate phenotypes (the so-called genetically determined metabotypes or GDMs) to reveal the biological mechanisms of genetics in human diseases. Here we conducted a two-sample Mendelian randomization analysis that uses GDMs to assess the causal effects of 486 human serum metabolites on 5 major psychiatric disorders, which respectively were schizophrenia (SCZ), major depression (MDD), bipolar disorder (BIP), autism spectrum disorder (ASD), and attention-deficit/hyperactivity disorder (ADHD). Using genetic variants as proxies, our study has identified 137 metabolites linked to the risk of psychiatric disorders, including 2-methoxyacetaminophen sulfate, which affects SCZ (P = 1.7 × 10–5) and 1-docosahexaenoylglycerophosphocholine, which affects ADHD (P = 5.6 × 10–5). Fourteen significant metabolic pathways involved in the 5 psychiatric disorders assessed were also detected, such as glycine, serine, and threonine metabolism for SCZ (P = .0238), Aminoacyl-tRNA biosynthesis for both MDD (P = .0144) and ADHD (P = .0029). Our study provided novel insights into integrating metabolomics with genomics in order to understand the mechanisms underlying the pathogenesis of human diseases.

Gamma-aminobutyric acid (GABA) and glutamate are implicated in the antidepressant effects of repetitive transcranial magnetic stimulation (rTMS), though findings from magnetic resonance spectroscopy (MRS) are inconsistent. Furthermore, the relationship between GABA A -receptor availability and rTMS outcomes remains largely unexplored. In this study, GABA and glutamate levels in the dorsal anterior cingulate cortex (dACC) were measured using a 1 H-MRS MEGA-PRESS sequence in 42 patients with bipolar or unipolar depression, both before and after a sham-controlled, double-blind clinical trial involving intermittent theta-burst stimulation (iTBS) over the dorsomedial prefrontal cortex. A subset of 28 patients also underwent [ 11 C]flumazenil positron emission tomography (PET) to measure whole-brain GABA A -receptor availability and mean receptor availability in the nucleus accumbens and dACC. Depressive symptoms were assessed using the self-rated Montgomery Åsberg Depression Rating Scale (MADRS-S). The results indicated no significant changes in neurotransmitter levels or GABA A -receptor availability post-iTBS in either the active or sham conditions. However, changes in MADRS-S scores after active iTBS were positively correlated with changes in GABA levels in the dACC (r(13) = 0.54, p  =  0.04 ) and baseline GABA A -receptor availability in the nucleus accumbens (r(11) = 0.66, p  =  0.02 ). These correlations were absent in the sham group. The findings suggest that a reduction in GABA within targeted frontostriatal circuits can be part of the antidepressant mechanism of iTBS, challenging previous research. Additionally, they indicate a potential predictive role for frontostriatal GABA A -receptor availability in the treatment of depression using dorsomedial prefrontal iTBS.

Adding supraphysiologic doses of levothyroxine (L-T4) to standard treatment for bipolar depression shows promise, but the mechanisms underlying clinical improvement are unknown. In a previous pilot study, L-T4 treatment reduced depression scores and activity within the anterior limbic network. Here we extended this work in a randomized, double-blind, placebo-controlled study of patients with bipolar depression. Cerebral glucose metabolism was assessed with positron emission tomography and [F-18]fluorodeoxyglucose before and after 6 weeks of treatment with L-T4 ( n =15) or placebo ( n =10) in 12 volumes of interest (VOIs): the bilateral thalamus, amygdala, hippocampus, dorsal striatum and ventral striatum, and midline cerebellar vermis and subgenual cingulate cortex. Radioactivity in the VOIs, normalized to whole-brain radioactivity was taken as a surrogate index of glucose metabolism, and markers of thyroid function were assayed. Changes in brain activity and their association with clinical response were assessed using statistical parametric mapping. Adjunctive L-T4 treatment produced a significant decline in depression scores during the 6-week treatment. In patients treated with L-T4, we found a significant decrease in regional activity at P <0.05 after Bonferroni correction in the left thalamus, right amygdala, right hippocampus, left ventral striatum and the right dorsal striatum. Decreases in the left thalamus, left dorsal striatum and the subgenual cingulate were correlated with a reduction in depression scores ( P <0.05 after Bonferroni correction). Placebo treatment was associated with a significant decrease in activity only in the right amygdala, and no region had a change in activity that was correlated with change in depression scores. The groups differed significantly in the relationship between the changes in depression scores and in activity in the thalamus bilaterally and the left ventral striatum. The findings provide evidence that administration of supraphysiologic thyroid hormone improves depressive symptoms in patients with bipolar disorder by modulating function in components of the anterior limbic network.

Bipolar disorder is a psychiatric disorder characterized by recurrent episodes of mania/hypomania and depression. Progressive cognitive dysfunction such as impairments in executive function and verbal memory is common in euthymic bipolar patients. The cerebrospinal fluid has previously been used to study neurodegenerative processes in Alzheimer's disease, from which changes in three core biomarkers have emerged as indicative of degeneration: amyloid β, total tau, and hyperphosphorylated tau. Here, neurodegeneration in bipolar disorder was investigated by assessing the association between bipolar disorder and cerebrospinal fluid biomarkers for neurodegenerative processes. Cerebrospinal fluid was obtained from 139 bipolar disorder patients and 71 healthy controls. Concentrations of total and phosphorylated tau, amyloid β1-42, amyloid β38/β40/β42, and the soluble forms of amyloid precursor protein were measured in patients vs controls. The concentrations of the soluble forms of amyloid precursor protein were significantly lower in bipolar patients compared with controls. The amyloid β42/amyloid β38 and the amyloid β42/amyloid β40 ratios were higher in bipolar patients than controls. There were no discernible differences in the concentrations of total/phosphorylated tau, amyloid β1-42, or amyloid β38/β40/β42. The concentrations of the biomarkers within the bipolar patient group were further associated with different ongoing medical treatments and diagnostic subgroups. The findings suggest that the amyloid precursor protein metabolism is altered in bipolar disorder. The results may have implications for the understanding of the pathophysiology of bipolar disorder and for the development of treatment strategies. Importantly, there were no signs of an Alzheimer-like neurodegenerative process among bipolar patients.

Inflammation is thought to be involved in the pathophysiology of bipolar disorder (BP) and metabolic syndrome. Prior studies evaluated the association between metabolic profiles and cytokines only during certain mood states instead of their changes during treatment. We enrolled drug-naïve patients with BP-II and investigated the correlation between changes in mood symptoms and metabolic indices with changes in plasma cytokine levels after 12 weeks of pharmacological treatment. Drug-naïve patients (n = 117) diagnosed with BP-II according to DSM-IV criteria were recruited. Metabolic profiles (cholesterol, triglyceride, HbA1C, fasting serum glucose, body mass index (BMI) and plasma cytokines (TNF-α, CRP, IL-6, and TGF-β) were measured at baseline and 2, 8, and 12 weeks post-treatment. To adjust within-subject dependence over repeated assessments, multiple linear regressions with generalized estimating equation methods were used. Seventy-six (65.0%) patients completed the intervention. Changes in plasma CRP were significantly associated with changes in BMI (P = 1.7E-7) and triglyceride (P = 0.005) levels. Changes in plasma TGF-β1 were significantly associated with changes in BMI (P = 8.2E-6), cholesterol (P = 0.004), and triglyceride (P = 0.006) levels. However, changes in plasma TNF-α and IL-6 were not associated with changes in any of the metabolic indices. Changes in Hamilton Depression Rating Scale scores were significantly associated with changes in IL-6 (P = 0.003) levels; changes in Young Mania Rating Scale scores were significantly associated with changes in CRP (P = 0.006) and TNF-α (P = 0.039) levels. Plasma CRP and TGF-β1 levels were positively correlated with several metabolic indices in BP-II after 12 weeks of pharmacological intervention. We also hypothesize that clinical symptoms are correlated with certain cytokines. These new findings might be important evidence that inflammation is the pathophysiology of clinical symptoms and metabolic disturbance in BP-II. ClinicalTrials.gov NCT01188148.

Quetiapine has been reported to prolong the QT interval, and has been used as a positive control in thorough QT studies. The objective of the present study was to evaluate, in the late stages of clinical development, the QT-prolongation effects of the extended-release (XR) formulation of quetiapine at the approved dose in Japanese patients with bipolar disorder, using concentration–QT modeling and simulation. Plasma concentrations of quetiapine and 4 of its metabolites (M1, M2, M4, and M5), and the QT interval corrected using the Fridericia formula (QTcF), were used for the concentration–QT analysis. Data from intensive electrocardiogram monitoring at predose and at 4, 6, 10, and 24 h after the administration of the last dose were pooled from a Phase I trial (6949-CL-0006) and from sparse sampling in late-stage clinical trials (6949-CL-0005, -0021, −0022, and −0023) in Japanese patients (N = 505). The upper limit of 1-sided 95% confidence interval (CI) of the changes from baseline in QTcF (ΔQTcF) at the geometric mean Cmax of a therapeutic dose of 300 mg once daily was predicted using a linear mixed-effects model, with the intercept as a random effect specifying a subject effect. For quetiapine and M2, but not M1, M4, or M5, positive slopes were observed between ΔQTcF and concentration. The predicted upper limits of the 1-sided 95% CIs did not exceed the regulatory threshold of 10 msec. Therefore, QTc prolongation is unlikely to be clinically relevant at the approved dose of quetiapine XR. In this pooled data analysis of the QT-prolongation effects of the quetiapine XR, positive relationships between ΔQTcF and quetiapine and M2 concentrations were observed. However, the predicted upper limits of the 1-sided 95% CIs did not exceed 10 msec. Therefore, QTc prolongation is unlikely to be clinically relevant at the approved dose. ClinicalTrials.gov identifiers: NCT01725282, NCT01919008, NCT01725308, NCT01737268, and NCT02362412.

We recently reported that the D2/D3 agonist pramipexole may have pro-cognitive effects in euthymic patients with bipolar disorder (BPD); however, the emergence of impulse-control disorders has been documented in Parkinson's disease (PD) after pramipexole treatment. Performance on reward-based tasks is altered in healthy subjects after a single dose of pramipexole, but its potential to induce abnormalities in BPD patients is unknown. We assessed reward-dependent decision making in euthymic BPD patients pre- and post 8 weeks of treatment with pramipexole or placebo by using the Iowa Gambling Task (IGT). The IGT requires subjects to choose among four card decks (two risky and two conservative) and is designed to promote learning to make advantageous (conservative) choices over time. Thirty-four BPD patients completed both assessments (18 placebo and 16 pramipexole). Baseline performance did not differ by treatment group (F=0.63; p=0.64); however, at week 8, BPD patients on pramipexole demonstrated a significantly greater tendency to make increasingly high-risk, high-reward choices across the five blocks, whereas the placebo group's pattern was similar to that reported in healthy individuals (treatment × time × block interaction, p<0.05). Analyses of choice strategy using the expectancy valence model revealed that after 8 weeks on pramipexole, BPD patients attended more readily to feedback related to gains than to losses, which could explain the impaired learning. There were no significant changes in mood symptoms over the 8 weeks, and no increased propensity toward manic-like behaviors were reported. Our results suggest that the enhancement of dopaminergic activity influences risk-associated decision-making performance in euthymic BPD. The clinical implications remain unknown.

The objectives of this study were to explore covariates of plasma quetiapine concentrations after oral administration of quetiapine extended-release formulation (XR), and to examine the exposure–response relationship in Japanese patients with bipolar depression, using population pharmacokinetics (PopPK) modeling. In a multicenter, randomized, double-blind, placebo-controlled study of quetiapine XR in patients with bipolar depression, plasma for the measurement of quetiapine concentration was collected at weeks 2, 4, 8, 12, 20, 28, and 52 during oral administration of 150 or 300 mg once daily of quetiapine XR before bedtime. A PopPK model of quetiapine XR was developed using nonlinear mixed-effects modeling with first-order conditional estimation with interactions. The exposure–response relationship was examined using post-hoc exposures. The post-hoc AUC estimate was plotted against the change in the Montgomery-Åsberg Depression Rating Scale (ΔMADRS) total score from baseline to 8 weeks following once-daily doses at 300 mg. The final PopPK analysis dataset contained 322 patients and 1162 observations (cutoff data at week 28; cutoff date, February 2016). The plasma quetiapine concentration–time profile in patients with bipolar depression after oral administration of quetiapine XR was represented well using a 1-compartment with first-order absorption model. Covariate analysis led to the selection of γ-glutamyl transpeptidase on apparent oral clearance and body weight on apparent volume of distribution as covariates. The final population mean values of apparent oral clearance and apparent volume of distribution were 87.7 L/h and 277 L, respectively, and the interindividual %CVs were 32.6% and 75.0%, respectively. The effects of covariates on PK parameters were not large compared with the interindividual variability. In addition, there was no clear relationship between the AUC and ΔMADRS. ClinicalTrials.gov identifier: NCT01725308.

Patients with subthreshold hypomania (SBP; subthreshold bipolar disorder) were indistinguishable from those with bipolar disorder (BP)-II on clinical bipolar validators, but their analyses lacked biological and pharmacological treatment data. Because inflammation and neuroprogression underlies BP, we hypothesized that cytokines and brain-derived neurotrophic factor (BDNF) are biomarkers for BP. We enrolled 41 drug-naïve patients with SBP and 48 with BP-II undergoing 12 weeks of pharmacological treatment (valproic acid, fluoxetine, risperidone, lorazepam). The Hamilton Depression Rating Scale (HDRS) and Young Mania Rating Scale (YMRS) were used to evaluate clinical responses at baseline and at weeks 0, 1, 2, 4, 8, and 12. Inflammatory cytokines (tumour necrosis factor [TNF]-α, transforming growth factor [TGF]-β1, interleukin [IL]-6, IL-8 and IL-1β) and BDNF levels were also measured. Mixed models repeated measurement was used to examine the therapeutic effect and changes in BDNF and cytokine levels between the groups. HDRS and YMRS scores significantly (P < 0.001) declined in both groups, the SBP group had significantly lower levels of BDNF (P = 0.005) and TGF-β1 (P = 0.02). Patients with SBP and BP-II respond similarly to treatment, but SBP patients may have different neuroinflammation marker expression.

Supplementation of standard treatment with high-dose levothyroxine (L-T 4 ) is a novel approach for treatment-refractory bipolar disorders. This study tested for effects on brain function associated with mood alterations in bipolar depressed patients receiving high-dose L-T 4 treatment adjunctive to ongoing medication (antidepressants and mood stabilizers). Regional activity and whole-brain analyses were assessed with positron emission tomography and [ 18 F]fluorodeoxyglucose in 10 euthyroid depressed women with bipolar disorder, before and after 7 weeks of open-label adjunctive treatment with supraphysiological doses of L-T 4 (mean dose 320  μ g/day). Corresponding measurements were acquired in an age-matched comparison group of 10 healthy women without L-T 4 treatment. The primary biological measures were relative regional activity (with relative brain radioactivity taken as a surrogate index of glucose metabolism) in preselected brain regions and neuroendocrine markers of thyroid function. Treatment-associated changes in regional activity (relative to global activity) were tested against clinical response. Before L-T 4 treatment, the patients exhibited significantly higher activity in the right subgenual cingulate cortex, left thalamus, medial temporal lobe (right amygdala, right hippocampus), right ventral striatum, and cerebellar vermis; and had lower relative activity in the middle frontal gyri bilaterally. Significant behavioral and cerebral metabolic effects accompanied changes in thyroid hormone status. L-T 4 improved mood (remission in seven patients; partial response in three); and decreased relative activity in the right subgenual cingulate cortex, left thalamus, right amygdala, right hippocampus, right dorsal and ventral striatum, and cerebellar vermis. The decrease in relative activity of the left thalamus, left amygdala, left hippocampus, and left ventral striatum was significantly correlated with reduction in depression scores. Results of the whole-brain analyses were generally consistent with the volume of interest results. We conclude that bipolar depressed patients have abnormal function in prefrontal and limbic brain areas. L-T 4 may improve mood by affecting circuits involving these areas, which have been previously implicated in affective disorders.