Elevated plasma orexin A levels in a subgroup of patients with schizophrenia associated with fewer negative and disorganized symptoms

Baseline prepulse inhibition dependency of orexin A and REM sleep deprivation

RATIONALE

Prepulse inhibition (PPI) impairment reflects sensorimotor gating problems, i.e. in schizophrenia. This study aims to enlighten the role of orexinergic regulation on PPI in a psychosis-like model.

OBJECTIVES

In order to understand the impact of orexinergic innervation on PPI and how it is modulated by age and baseline PPI (bPPI), chronic orexin A (OXA) injections was carried on non-sleep-deprived and sleep-deprived rats that are grouped by their bPPI.

METHODS

bPPI measurements were carried on male Wistar rats on P45 or P90 followed by grouping into low-PPI and high-PPI rats. The rats were injected with OXA twice per day for four consecutive days starting on P49 or P94, while the control groups received saline injections. 72 h REMSD was carried on via modified multiple platform technique on P94 and either OXA or saline was injected during REMSD. PPI tests were carried out 30 min. after the last injection.

RESULTS

Our previous study with acute OXA injection after REMSD without bPPI grouping revealed that low OXA doses might improve REMSD-induced PPI impairment. Our current results present three important conclusions: (1) The effect of OXA on PPI is bPPI-dependent and age-dependent. (2) The effect of REMSD is bPPI-dependent. (3) The effect of OXA on PPI after REMSD also depends on bPPI.

CONCLUSION

Orexinergic regulation of PPI response with and without REMSD can be predicted by bPPI levels. Our findings provide potential insights into the regulation of sensorimotor gating by sleep/wakefulness systems and present potential therapeutic targets for the disorders, where PPI is disturbed.

Discovery and first-time disclosure of CVN766, an exquisitely selective orexin 1 receptor antagonist

Modulators of orexin receptors are being developed for neurological illnesses such as sleep disorders, addictive behaviours and other psychiatric diseases. We herein describe the discovery of CVN766, a potent orexin 1 receptor antagonist that has greater than 1000-fold selectivity for the orexin 1 receptor over the orexin 2 receptor and demonstrates low off target hits in a diversity screen. In agreement with its in vitro ADME data, CVN766 demonstrated moderate in vivo clearance in rodents and displayed good brain permeability and target occupancy. This drug candidate is currently being investigated in clinical trials for schizophrenia and related psychiatric conditions.

Higher orexin-A levels are associated with treatment response to clozapine in patients with schizophrenia: A cross-sectional study

BACKGROUND

Clozapine is the primary antipsychotic (APD) for treatment-resistant schizophrenia (TRS). However, only 40% of patients with TRS respond to clozapine, constituting a subgroup of clozapine-resistant patients. Recently, the neuropeptide orexin-A was shown to be involved in the pathophysiology of schizophrenia. This study evaluated the association of orexin-A levels with the clozapine response in patients with TRS.

METHODS

We recruited 199 patients with schizophrenia, including 37 APD-free and 162 clozapine-treated patients. Clozapine-treated patients were divided into clozapine-responsive (n = 100) and clozapine-resistant (n = 62) groups based on whether they had achieved psychotic remission defined by the 18-item Brief Psychiatric Rating Scale (BPRS-18). We compared blood orexin-A levels among the three groups and performed regression analysis to determine the association of orexin-A level with treatment response in clozapine-treated patients. We also explored the correlation between orexin-A levels and cognitive function, assessed using the CogState Schizophrenia Battery.

RESULTS

Clozapine-responsive patients had higher orexin-A levels than clozapine-resistant and APD-free patients. Orexin-A level was the only factor significantly associated with treatment response after adjustment. Orexin-A levels were negatively correlated with BPRS-18 full scale and positive, negative, and general symptoms subscale scores. We also observed a positive correlation between orexin-A levels and verbal memory, visual learning and memory, and working memory function.

CONCLUSIONS

This cross-sectional study showed that higher levels of orexin-A are associated with treatment response to clozapine in patients with TRS. Future prospective studies examining changes in orexin-A level following clozapine treatment and the potential benefit of augmenting orexin-A signaling are warranted.

Nurse-led lifestyle intervention in a cohort of schizophrenia patients treated with clozapine

Patients diagnosed with schizophrenia are characterized by early mortality compared to the general population. The main cause of this premature death reflects medical complications linked to metabolic syndrome (MetS). The use of antipsychotics such as clozapine is associated with weight gain and metabolic disturbances in certain predisposed individuals. Non-pharmacological interventions for weight control have become a key element for secondary prevention in the health of patients diagnosed with schizophrenia. Here, we aim to evaluate the physical health effects of a nurse-led non-pharmacological intervention program in patients with a diagnosis of schizophrenia treated with clozapine. Thirty-one outpatients from the outpatient clinical facility of Hospital Clinic in Barcelona, Spain diagnosed with schizophrenia and other psychotic disorders receiving clozapine treatment were enrolled in a prospective interventional study, comprising an 8-week group program of therapeutic education in a healthy lifestyle. MetS factors, physical activity, diet, and lifestyle were evaluated at baseline, post-intervention (8 weeks), and 3 months after the program. Weight, body mass index, high-density lipoprotein cholesterol, and diet patterns displayed significant differences post-intervention and after 3 months, while only waist, hip perimeter, and lifestyle improved post-intervention. Our results suggest the effectiveness of the lifestyle intervention in patients under clozapine treatment despite its long-time differential effect. Strategies to prevent weight gain and metabolic decline will help prevent premature cardiometabolic disease in this vulnerable population.

Dual orexin/hypocretin receptor antagonism attenuates NMDA receptor hypofunction-induced attentional impairments in a rat model of schizophrenia

Schizophrenia is a neuropsychiatric condition that is associated with impaired attentional processing and performance. Failure to support increasing attentional load may result, in part, from inhibitory failure in attention-relevant cortical regions, and available antipsychotics often fail to address this issue. Orexin/hypocretin receptors are found throughout the brain and are expressed on neurons relevant to both attention and schizophrenia, highlighting them as a potential target to treat schizophrenia-associated attentional dysfunction. In the present experiment, rats (N = 14) trained in a visual sustained attention task that required discrimination of trials which presented a visual signal from trials during which no signal was presented. Once trained, rats were then co-administered the psychotomimetic N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine (MK-801: 0 or 0.1 mg/kg, intraperitoneal injections) and the dual orexin receptor antagonist filorexant (MK-6096: 0, 0.1, or 1 mM, intracerebroventricular infusions) prior to task performance across six sessions. Dizocilpine impaired overall accuracy during signal trials, slowed reaction times for correctly-responded trials, and increased the number of omitted trials throughout the task. Dizocilpine-induced increases in signal trial deficits, correct response latencies, and errors of omission were reduced following infusions of the 0.1 mM, but not 1 mM, dose of filorexant. As such, orexin receptor blockade may improve attentional deficits in a state of NMDA receptor hypofunction.

Nasal administration of orexin A partially rescues dizocilpine-induced cognitive impairments in female C57BL/6J mice

Sex difference has been reported in several behavioural endophenotypes of neuropsychiatric disorder in both rodents and humans. However, sex difference in cognitive symptoms associated with neuropsychiatric disorders has not been studied in detail. In this study, we induced cognitive impairment using the NMDA receptor antagonist, dizocilpine (MK-801), in male and female C57BL/6J mice and performed a visual discrimination task in an automated touchscreen system. We found that discrimination performance decreased with increased doses of MK-801 in both sexes. However, female mice showed stronger deficit in discrimination performance than the male mice especially after administration of low (0.01mg/kg) and high (0.15mg/kg) doses of MK-801. Furthermore, we tested if administration of orexin A, orexin-1 receptor antagonist SB-334867 or orexin-2 receptor antagonist EMPA rescued MK-801 (0.15mg/kg) induced cognitive impairment in visual discrimination. We found that nasal administration of orexin A partially rescued the cognitive impairment induced by MK-801 in females but not in males. Taken together, our data show that female C57BL/6J mice are more sensitive compared to males to some doses of MK-801 in discrimination learning task and that orexin A partially rescues this cognitive impairment in females.

Targeting the orexin/hypocretin system for the treatment of neuropsychiatric and neurodegenerative diseases: from animal to clinical studies

Orexins (also known as hypocretins) are neuropeptides located exclusively in hypothalamic neurons that have extensive projections throughout the central nervous system and bind two different G protein-coupled receptors (OX1R and OX2R). Since its discovery in 1998, the orexin system has gained the interest of the scientific community as a potential therapeutic target for the treatment of different pathological conditions. Considering previous basic science research, a dual orexin receptor antagonist, suvorexant, was the first orexin agent to be approved by the US Food and Drug Administration to treat insomnia. In this review, we discuss and update the main preclinical and human studies involving the orexin system with several psychiatric and neurodegenerative diseases. This system constitutes a nice example of how basic scientific research driven by curiosity can be the best route to the generation of new and powerful pharmacological treatments.

Psychotic Episode and Schizophrenia in Slovakian Narcolepsy Database

Narcolepsy type 1 (NT1), a central disorder of hypersomnolence, is associated with mood, anxiety or hyperactivity mental disorders. Association with psychotic episode or schizophrenia is rare and could be the source of diagnostic and therapeutic difficulties. Their frequency in the national narcolepsy database has not been systematically studied. The aim of the presented study was to calculate the frequency of NT1 patients diagnosed with psychosis and/or schizophrenia, to identify clinical characteristics of these cases, and to look for narcoleptic and psychotic symptoms during re-evaluation years later. We identified three (4%) cases diagnosed with a psychotic episode in the course of NT1. They were diagnosed with NT1 by age ≤18 years. In the re-evaluation (mean follow-up 9.8 years), we identified one case with a dual diagnosis of NT1 and schizophrenia; two cases were diagnosed with a solitary psychotic episode in the course of NT1. NT1 patients diagnosed in the age ≤18 years are at higher risk of psychotic episode, and this may be related to higher vulnerability during the ongoing neurodevelopmental period. Comorbid schizophrenia with NT1 in the Slovakian Narcolepsy Database was within the prevalence expected in the general population. The solitary psychotic episode in the course of NT1 did not reduce the possibility of subsequent symptomatic treatment afterwards.

Orexin deficiency affects sensorimotor gating and its amphetamine-induced impairment

The orexin neuropeptides have an important role in the regulation of the sleep/wake cycle and foraging, as well as in reward processing and emotions. Furthermore, recent research implicates the orexin system in different behavioral endophenotypes of neuropsychiatric diseases such as social avoidance and cognitive flexibility. Utilizing orexin-deficient mice, the present study tested the hypothesis that orexin is involved in two further mouse behavioral endophenotypes of neuropsychiatric disorders, i.e., sensorimotor gating and amphetamine sensitivity. The data revealed that orexin-deficient mice expressed a deficit in sensorimotor gating, measured by prepulse inhibition of the startle response. Amphetamine treatment impaired prepulse inhibition in wildtype and heterozygous orexin-deficient mice, but had no effects in homozygous orexin-deficient mice. Furthermore, locomotor activity and center time in the open field was not affected by orexin deficiency but was similarly increased or decreased, respectively, by amphetamine treatment in all genotypes. These data indicate that the orexin system modulates prepulse inhibition and is involved in mediating amphetamine's effect on prepulse inhibition. Future studies should investigate whether pharmacological manipulations of the orexin system can be used to treat neuropsychiatric diseases associated with deficits in sensorimotor gating, such as schizophrenia or attention deficit hyperactivity disorder.

Correlation of Orexin-A and brain-derived neurotrophic factor levels in metabolic syndrome and cognitive impairment in schizophrenia treated with clozapine

Orexin-A and brain-derived neurotrophic factor (BDNF) are implicated in regulating metabolic syndrome (MetS) and cognitive impairment of schizophrenia. However, the associations among them remains unclear. Here, we aimed to investigate the relationship between Orexin-A levels, BDNF, MetS, clinical symptom profile, and cognitive function in schizophrenia patients following long-term clozapine treatment. We measured Orexin-A and BDNF levels in 140 schizophrenia patients with and without MetS. We assessed clinical symptoms on the Positive and Negative Syndrome Scale and cognitive function by the assessment of Neuropsychological Status (RBANS), and examined their associations with Orexin-A. Patients with MetS had significantly lower Orexin-A levels and higher coding test, attention span and delayed retention in RBANS (P < 0.05). Correlation analysis showed that Orexin-A was associated with BDNF, TG, HDLC, PANSS active social avoidance and emotional withdrawal significantly. Besides, Orexin-A significantly interacted with BDNF for metabolic and cognitive profiles including waist circumference, delayed retention and list recognition. Logistic regression analysis showed that Orexin-A level (odds ratio [OR]= 0.380, 95% confidence interval [CI]: 0.151-0.952, P = 0.039) and total illness duration (OR = 0.932, 95% CI: 0.875-0.991, P = 0.025) were predictive variables of MetS. However, there was no significant relationship between Orexin-A and cognitive function after adjustment for age, sex and educational levels. Totally, a lower plasma Orexin-A level seems to be related to metabolic parameters more than cognitive profiles. The interaction of Orexin-A with BDNF may be partly responsible for worse MetS and better cognition of elderly schizophrenia, but the causal relationship needs further clarification.

Orexin-a elevation in antipsychotic-treated compared to drug-free patients with schizophrenia: A medication effect independent of metabolic syndrome

BACKGROUND/PURPOSE

Orexin-A levels are reportedly increased in antipsychotic (APD)-treated patients with schizophrenia compared to healthy controls and have been associated with metabolic abnormalities. It is not clear whether the orexin-A elevation is related specifically to the drug (APDs) effect, which should be clarified by including a drug-free group for comparison, or related to drug-induced metabolic abnormalities.

METHODS

Blood orexin-A levels and metabolic profiles were compared between 37 drug-free, 45 aripiprazole-treated, and 156 clozapine-treated patients with schizophrenia. The association between orexin-A and metabolic outcomes were examined. We explored the effects of APDs treatment and metabolic status on orexin-A levels by linear regression.

RESULTS

Patients under APDs treatment had increased orexin-A levels compared to drug-free patients, with aripiprazole-treated group having higher orexin-A levels than clozapine-treated group. Higher orexin-A levels reduced the risks of metabolic syndrome (MS) and type 2 diabetes mellitus, indicating a relationship between orexin-A levels and metabolic problems. After adjusting the effect from metabolic problems, we found APD treatment is still associated with orexin-A regulation, with aripiprazole more significantly than clozapine.

CONCLUSION

With the inclusion of drug-free patients rather than healthy controls for comparison, we demonstrated that orexin-A is upregulated following APD treatment even after we controlled the potential effect from MS, suggesting an independent effect of APDs on orexin-A levels. Furthermore, the effect differed between APDs with dissimilar obesogenicity, i.e. less obesogenicity likely associated with higher orexin-A levels. Future prospective studies exploring the causal relationship between APDs treatment and orexin-A elevation as well as the underlying mechanisms are warranted.

Neurobiology of the Orexin System and Its Potential Role in the Regulation of Hedonic Tone

Orexin peptides comprise two neuropeptides, orexin A and orexin B, that bind two G-protein coupled receptors (GPCRs), orexin receptor 1 (OXR1) and orexin receptor 2 (OXR2). Although cell bodies that produce orexin peptides are localized in a small area comprising the lateral hypothalamus and adjacent regions, orexin-containing fibres project throughout the neuraxis. Although orexins were initially described as peptides that regulate feeding behaviour, research has shown that orexins are involved in diverse functions that range from the modulation of autonomic functions to higher cognitive functions, including reward-seeking, behaviour, attention, cognition, and mood. Furthermore, disruption in orexin signalling has been shown in mood disorders that are associated with low hedonic tone or anhedonia, including depression, anxiety, attention deficit hyperactivity disorder, and addiction. Notably, projections of orexin neurons overlap circuits involved in the modulation of hedonic tone. Evidence shows that orexins may potentiate hedonic behaviours by increasing the feeling of pleasure or reward to various signalling, whereas dysregulation of orexin signalling may underlie low hedonic tone or anhedonia. Further, orexin appears to play a key role in regulating behaviours in motivationally charged situations, such as food-seeking during hunger, or drug-seeking during withdrawal. Therefore, it would be expected that dysregulation of orexin expression or signalling is associated with changes in hedonic tone. Further studies investigating this association are warranted.

Plasma Orexin-A Levels in Patients With Schizophrenia: A Systematic Review and Meta-Analysis

BACKGROUND

Orexins are polypeptides regulating appetite, sleep-wake cycle, and cognition functions, which are commonly disrupted in patients with schizophrenia. Patients with schizophrenia show a decreased connectivity between the prefrontal cortex and midline-anterior thalamus, and orexin can directly activate the axon terminal of cells within the prefrontal cortex and selectively depolarize neurons in the midline intralaminar nuclei of the thalamus. To address the relationship between orexin and schizophrenia, this study performed a meta-analysis on the alteration of plasma orexin-A levels in patients with schizophrenia.

METHOD

We searched eligible studies in PubMed, Embase, Cochrane, and China National Knowledge Infrastructure (CNKI) from 1998 to September 3, 2021. A total of 8 case-control studies were included in the meta-analyses, providing data on 597 patients with schizophrenia and 370 healthy controls. The Stata version 16.0 software was used to calculate the Hedges's adjusted g with 95% confidence intervals (CI).

RESULTS

The plasma orexin-A levels were not altered in subjects with schizophrenia (n = 597) when compared to healthy controls (n = 370). Subgroup analyses of gender (male and female vs. only male), country (China vs. other countries), medication (medication vs. non-medication), and the measurement of plasma orexin-A (Enzyme-linked immunosorbent assay vs. radioimmunoassay) revealed heterogeneity ranging from 30.15 to 98.15%, but none showed a significant alteration of plasma orexin-A levels in patients with schizophrenia. Heterogeneity was lower in the other countries and radioimmunoassay subgroup, while other subgroups remained to be highly heterogeneous. No significant evidence of publication bias was found either in Begg's test or the Egger's test.

CONCLUSION

The present meta-analysis indicated that patients with schizophrenia did not show abnormal plasma levels of orexin-A.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021283455, identifier: CRD42021283455.

Dissociative Effects of Neuropeptide S Receptor Deficiency and Nasal Neuropeptide S Administration on T-Maze Discrimination and Reversal Learning

Cognitive flexibility refers to the ability to modify learned behavior in response to changes in the environment. In laboratory rodents, cognitive flexibility can be assessed in reversal learning, i.e., the change of contingencies, for example in T-maze discrimination learning. The present study investigated the role of the neuropeptide S (NPS) system in cognitive flexibility. In the first experiment, mice deficient of NPS receptors (NPSR) were tested in T-maze discrimination and reversal learning. In the second experiment, C57BL/6J mice were tested in the T-maze after nasal administration of NPS. Finally, the effect of nasal NPS on locomotor activity was evaluated. NPSR deficiency positively affected the acquisition of T-maze discrimination but had no effects on reversal learning. Nasal NPS administration facilitated reversal learning and supported an allocentric learning strategy without affecting acquisition of the task or locomotor activity. Taken together, the present data show that the NPS system is able to modulate both acquisition of T-maze discrimination and its reversal learning. However, NPSR deficiency only improved discrimination learning, while nasal NPS administration only improved reversal learning, i.e., cognitive flexibility. These effects, which at first glance appear to be contradictory, could be due to the different roles of the NPS system in the brain regions that are important for learning and cognitive flexibility.

Changes of Hypocretin (Orexin) System in Schizophrenia: From Plasma to Brain

Hypocretin (also called orexin) regulates various functions, such as sleep-wake rhythms, attention, cognition, and energy balance, which show significant changes in schizophrenia (SCZ). We aimed to identify alterations in the hypocretin system in SCZ patients. We measured plasma hypocretin-1 levels in SCZ patients and healthy controls and found significantly decreased plasma hypocretin-1 levels in SCZ patients, which was mainly due to a significant decrease in female SCZ patients compared with female controls. In addition, we measured postmortem hypothalamic hypocretin-1-immunoreactivity (ir), ventricular cerebrospinal fluid (CSF) hypocretin-1 levels, and hypocretin receptor (Hcrt-R) mRNA expression in the superior frontal gyrus (SFG) in SCZ patients and controls We observed a significant decrease in the amount of hypothalamic hypocretin-1 ir in SCZ patients, which was due to decreased amounts in female but not male patients. Moreover, Hcrt-R2 mRNA in the SFG was decreased in female SCZ patients compared with female controls, while male SCZ patients showed a trend of increased Hcrt-R1 mRNA and Hcrt-R2 mRNA expression compared with male controls. We conclude that central hypocretin neurotransmission is decreased in SCZ patients, especially female patients, and this is reflected in the plasma.

Targeting the microbiome-gut-brain axis for improving cognition in schizophrenia and major mood disorders: A narrative review

Cognitive impairment has been consistently found to be a core feature of serious mental illnesses such as schizophrenia and major mood disorders (major depression and bipolar disorder). In recent years, a great effort has been made in elucidating the biological causes of cognitive deficits and the search for new biomarkers of cognition. Microbiome and gut-brain axis (MGB) hormones have been postulated to be potential biomarkers of cognition in serious mental illnesses. The main aim of this review was to synthesize current evidence on the association of microbiome and gut-brain hormones on cognitive processes in schizophrenia and major mood disorders and the association of MGB hormones with stress and the immune system. Our review underscores the role of the MGB axis on cognitive aspects of serious mental illnesses with the potential use of agents targeting the gut microbiota as cognitive enhancers. However, the current evidence for clinical trials focused on the MGB axis as cognitive enhancers in these clinical populations is scarce. Future clinical trials using probiotics, prebiotics, antibiotics, or faecal microbiota transplantation need to consider potential mechanistic pathways such as the HPA axis, the immune system, or gut-brain axis hormones involved in appetite control and energy homeostasis.

A higher body mass index in Chinese inpatients with chronic schizophrenia is associated with elevated plasma orexin-A levels and fewer negative symptoms

Objective: Orexin-A is involved in numerous physiological functions, such as feeding behavior and energy balance. Yet, the associations among the orexin system, weight changes and the clinical symptoms of schizophrenia patients remain uncertain, especially in inpatients with chronic schizophrenia (CS). The purpose of this study was to investigate the relationship between the orexin-A levels, body mass index (BMI) and clinical symptoms of CS inpatients.Methods: Altogether, 324 inpatients were enrolled in our study. The clinical symptoms of all inpatients were measured using a 30-item Positive and Negative Syndrome Scale (PANSS), and then we calculated the BMI of each subject and tested the orexin-A levels by ELISA methods.Results: The orexin-A levels of the CS inpatients in the obesity group (1.24 ± 1.45 ng/ml, n = 52) were significantly higher than those in the non-overweight group (0.85 ± 1.18 ng/ml, n = 176) and the overweight group (0.97 ± 1.15 ng/ml, n = 96). Spearman's correlation analysis showed that higher BMIs were associated with higher plasma orexin-A levels and fewer negative symptoms. Furthermore, the multiple regression analysis indicated that the orexin-A level could be a contributor to BMI (F = 30.21, p < 0.001). However, there was no correlation between plasma orexin-A concentrations and clinical symptoms in our research.Conclusion: A higher plasma orexin-A level may be a factor influencing the BMI of inpatients with CS, and fewer negative symptoms seem to be correlated with higher BMI, but the causality among BMI, orexin-A and clinical symptoms of schizophrenia requires further clinical research.

Impaired hormonal regulation of appetite in schizophrenia: A narrative review dissecting intrinsic mechanisms and the effects of antipsychotics

Cardiometabolic diseases are the main contributor of reduced life expectancy in patients with schizophrenia. It is now widely accepted that antipsychotic treatment plays an important role in the development of obesity and its consequences. However, some intrinsic mechanisms need to be taken into consideration. One of these mechanisms might be related to impaired hormonal regulation of appetite in this group of patients. In this narrative review, we aimed to dissect impairments of appetite-regulating hormones attributable to intrinsic mechanisms and those related to medication effects. Early hormonal alterations that might be associated with intrinsic mechanisms include low levels of leptin and glucagon-like peptide-1 (GLP-1) together with elevated insulin levels in first-episode psychosis (FEP) patients. However, evidence regarding low GLP-1 levels in FEP patients is based on one large study. In turn, multiple-episode schizophrenia patients show elevated levels of insulin, leptin and orexin A together with decreased levels of adiponectin. In addition, patients receiving olanzapine may present with low ghrelin levels. Post mortem studies have also demonstrated reduced number of neuropeptide Y neurons in the prefrontal cortex of patients with schizophrenia. Treatment with certain second-generation antipsychotics may also point to these alterations. Although our understanding of hormonal regulation of appetite in schizophrenia has largely been improved, several limitations and directions for future studies need to be addressed. This is of particular importance since several novel pharmacological interventions for obesity and diabetes have already been developed and translation of these developments to the treatment of cardiometabolic comorbidities in schizophrenia patients is needed.

Controlled sleep deprivation as an experimental medicine model of schizophrenia: An update

In recent years there has been a surge of interest and corresponding accumulation of knowledge about the role of sleep disturbance in schizophrenia. In this review, we provide an update on the current status of experimentally controlled sleep deprivation (SD) as an experimental medicine model of psychosis, and also consider, given the complexity and heterogeneity of schizophrenia, whether this (state) model can be usefully combined with other state or trait model systems to more powerfully model the pathophysiology of psychosis. We present evidence of dose-dependent aberrations that qualitatively resemble positive, negative and cognitive symptoms of schizophrenia as well as deficits in a range of translational biomarkers for schizophrenia, including prepulse inhibition, smooth pursuit and antisaccades, following experimentally controlled SD, relative to standard sleep, in healthy volunteers. Studies examining the combination of SD and schizotypy, a trait model of schizophrenia, revealed only occasional, task-dependent superiority of the combination model, relative to either of the two models alone. Overall, we argue that experimentally controlled SD is a valuable experimental medicine model of schizophrenia to advance our understanding of the pathophysiology of the clinical disorder and discovery of more effective or novel treatments. Future studies are needed to test its utility in combination with other, especially state, model systems of psychosis such as ketamine.

Plasma neuropeptides as circulating biomarkers of multifactorial schizophrenia

BACKGROUND

Promising biomarkers would be used to improve the determination of diagnosis and severity, as well as the prediction of symptomatic and functional outcomes of schizophrenia.

BASIC PROCEDURES

In this study, we used three different mouse models induced by a genetic factor (PV-Cre; ErbB4^-/-, G group), an environmental stressor (adolescent social isolation, G group), and a combination of genetic factor and environmental stressor (PV-Cre; ErbB4^-/- mice with isolation, G × E group). Attenuated PPI (%) confirmed the successful establishment of three schizophrenia-like mouse models. To evaluate whether neuropeptide levels in plasma would be potential biomarkers of different schizophrenia models in our work, we used MILLIPLEX® MAP method to simultaneously measure 6 critical neuropeptides in plasma.

MAIN FINDINGS

Among the evaluated neuropeptides, increased neurotensin tends to be associated with genetic factors of schizophrenia, increased orexin A seems to be a biomarker of an interplay between genetic and social isolation, while higher plasma oxytocin might be more apt to be responsive to social isolation. The potential biomarkers are mostly independent of sex.

CONCLUSIONS

This research would provide novel clues to develop circulating biomarkers of plasma neuropeptides for multifactorial schizophrenia.

Reduced plasma orexin-A levels in patients with bipolar disorder

PURPOSE

Orexins are hypothalamic neuropeptides involved in the regulation of sleep, appetite and arousal. An altered orexin system has been implicated in the pathophysiology of psychiatric disorders. This study aimed to examine whether plasma orexin-A levels differ in patients with schizophrenia, major depressive disorder (MDD), or bipolar disorder (BD) compared to in healthy controls. We also examined the possible correlations between plasma orexin-A levels and clinical variables.

PATIENTS AND METHODS

All participants were Japanese. The sample consisted of 80 patients with schizophrenia (42 women, 52.5%; mean age 36.8 years), 80 patients with MDD (43 women, 53.8%; 43.7 years), and 40 patients with BD (24 women, 60%; 41.1 years), as well as 80 healthy controls (48 women, 60%; 47.0 years). Plasma orexin-A levels were quantified by an enzyme-linked immunosorbent assay.

RESULTS

Mean orexin-A levels were significantly different across the four diagnostic groups (F=4.09; df=3; p=0.007, η2 =0.06). In particular, the patients with BD showed significantly lower orexin-A levels than did the controls. When the median value of the control group (109.8 pg/ml) was set as a cut-off value, subjects whose orexin-A levels were below the cut-off were more common in all psychiatric groups (schizophrenia: 73.8%, x2 =9.56, df=1, p=0.003, OR=2.81, 95% CI: 1.45 to 5.45, d=0.57; MDD: 78.5%, x2 =14.02, df=1, p<0.001, OR=3.65, 95% CI: 1.82 to 7.29, d=0.72; BD: 87.5%, x2 =16.0, df=1, p<0.001, OR=7.00, 95% CI: 2.49 to 19.70, d=1.07). We found no association between plasma orexin-A levels and any clinical symptoms, depression severity, or medication doses.

CONCLUSION

Our results suggest that plasma orexin-A levels are reduced in patients with BD.

Insomnia in patients with schizophrenia: current understanding and treatment options

In patients with schizophrenia, insomnia is a common yet often overlooked comorbidity. With sleep disturbances inextricably linked to increased severity of schizophrenia and worsening clinical outcomes, insomnia is an important therapeutic target within this patient population. Thus, through a review of the current literature, this paper reiterates the important etiological link between these two conditions, while evaluating the safety, efficacy, and limitations of current therapeutic options for the treatment of comorbid insomnia in schizophrenia. Despite the continued use of benzodiazepine receptor agonists (BZRAs) for insomnia, the use of other therapies such as Cognitive Behavioral Therapy for Insomnia (CBT-I) and suvorexant warrants increased consideration. More large-scale clinical trials are needed to assess the efficacy of such therapeutic options in the schizophrenia patient population.

Reduced Plasma Orexin-A Concentrations are Associated with Cognitive Deficits in Anorexia Nervosa

Orexins/hypocretins are neuropeptides implicated in numerous processes, including food intake and cognition. The role of these peptides in the psychopathology of anorexia nervosa (AN) remains poorly understood. The aim of the current study was to evaluate the associations between plasma orexin-A (OXA) concentrations and neuropsychological functioning in adult women with AN, and a matched control group. Fasting plasma OXA concentrations were taken in 51 females with AN and in 51 matched healthy controls. Set-shifting was assessed using the Wisconsin Card Sorting Test (WCST), whereas decision making was measured using the Iowa Gambling Task (IGT). The AN group exhibited lower plasma OXA levels than the HC group. Lower mean scores were obtained on the IGT in AN patients. WCST perseverative errors were significantly higher in the AN group compared to HC. In both the AN and HC group, OXA levels were negatively correlated with WCST non-perseverative errors. Reduced plasma OXA concentrations were found to be associated with set-shifting impairments in AN. Taking into consideration the function of orexins in promoting arousal and cognitive flexibility, future studies should explore whether orexin partly underpins the cognitive impairments found in AN.

Weight gain and metabolic change as predictors of symptom improvement in first-episode schizophrenia spectrum disorder patients treated over 12 months

BACKGROUND

Treatment-emergent weight gain is associated with antipsychotic efficacy in schizophrenia patients treated with clozapine and olanzapine. However, few studies have investigated this relationship in first-episode patients treated with other antipsychotics, in particular those with a lower obesogenic potential. Aim To investigate the relationships between weight gain and associated metabolic changes with psychopathology improvement in relation to age, sex, ethnicity, substance use, treatment duration and antipsychotic dose in first-episode schizophrenia spectrum disorder patients.

METHODS

This single site cohort study included 106 minimally treated or antipsychotic-naive patients treated with flupenthixol decanoate over 12 months. Psychopathology was evaluated using the Positive and Negative Syndrome Scale (PANSS) and BMI, fasting blood lipids and glucose were assessed at regular intervals. Linear regression models were constructed to determine the effects of socio-demographic, clinical and metabolic factors as predictors of change in total PANSS score and factor-derived domains.

RESULTS

BMI change scores were inversely correlated with change in PANSS total (R = -0.25; p = 0.011), positive (R = -0.23; p = 0.019), depressive anxiety (R = -0.21; p = 0.031) and disorganized symptoms (R = -0.32; p < 0.001). Linear regression analysis showed that increased BMI and treatment duration both predicted improvement in global psychopathology and disorganized symptoms independent of age, sex, ethnicity, substance use, co-medication with antidepressants and/or anticholinergics, as well as the dose and duration of antipsychotic exposure.

CONCLUSIONS

Our findings suggest that the relationship between treatment-emergent weight gain and psychopathology improvement is not limited to patients treated with antipsychotics most associated with weight gain, and is not confounded by treatment duration and dose.

Changes In Plasma NPY, IL-1β And Hypocretin In People Who Died By Suicide

PURPOSE

There is growing evidence showing that inflammatory cytokines and neuropeptides may be involved in the pathophysiology of suicidal behavior. However, studies have yielded contradictory data, and no biological markers that help predict suicide have been identified. This study aimed to identify biological patterns, such as NPY, IL-1β and hypocretin plasma levels, in people who died by suicide.

PATIENTS AND METHODS

Twenty-two people who died by suicide compared with 22 controls matched for age and sex were studied. In suicide and control subjects, we estimated the levels of NPY, IL-1β and hypocretin in plasma using enzyme-linked immunosorbent assay. The data are presented as the median (25th-75th percentile).

RESULTS

We found (1) a significant elevation in plasma NPY levels in suicide subjects versus control subjects (suicide: 11.38 (9.380-16.55); controls: 8.95 (7.590-10.93); P=0.013), and plasma NPY concentrations were approximately 62% higher in suicide subjects than those in control subjects; (2) a significant decrease in plasma IL-1β concentrations between suicide and control subjects (suicide: 121.1 (82.97-143.0); controls: 425.9 (233.1-835.3); P<0.001) as well as a decrease in IL-1β concentrations by almost 80%; and (3) no significant difference in plasma hypocretin levels between suicide and control subjects (suicide: 16.62 (13.62-25.77); controls: 21.63 (14.97-29.72); P=0.356).

CONCLUSION

Our results suggest that plasma NPY and IL-1β were related with suicide behavior rather than to suicide causes or suicide method. Specific combinations of plasma biomarkers may discriminate between types of suicidal behaviors and indicate increased risk for future suicide attempts.

Antipsychotics-induced metabolic alterations: Recounting the mechanistic insights, therapeutic targets and pharmacological alternatives

Atypical antipsychotics (AAPs) are the drug of choice in the management of mental illnesses by virtue of their advantage over typical antipsychotics i.e. least tendency of producing extrapyramidal motor symptoms (EPS) or pseudoparkinsonism. Despite the clinical efficacy, AAPs produces troublesome adverse effects, particularly hyperphagia, hyperglycemia, dyslipidemia weight gain, diabetes mellitus, insulin resistance and QT prolongation which further develops metabolic and cardiac complications with subsequent reduction in life expectancy, poor patient compliance, and sudden death. AAPs-induced weight gain and metabolic alterations are increasing at an alarming rate and became an utmost matter of concern for psychopharmacotherapy. Diverse underlying mechanisms have been explored such as the interaction of AAPs with neurotransmitter receptors, alteration in food reward anticipation behavior, altered expressions of hypothalamic orexigenic and anorexigenic neuropeptides, histamine H₁ receptor-mediated hypothalamic AMP-activated protein kinase (AMPK) activation, increased blood leptin, ghrelin, pro-inflammatory cytokines. Antipsychotics induced imbalance in energy homeostasis, reduction in energy expenditure which is linked to altered expression of uncoupling proteins (UCP-1) in brown adipose tissue and reduced hypothalamic orexin expressions are emerging insights. In addition, alteration in gut-microbiota and subsequent inflammation, dyslipidemia, obesity, and diabetes after AAPs treatment are also associated with weight gain and metabolic alterations. Oral hypoglycemics and lipid-lowering drugs are mainly prescribed in the clinical management of weight gain associated with AAPs while many other pharmacological and nonpharmacological interventions also have been explored in different clinical and preclinical studies. In this review, we critically discuss the current scenario, mechanistic insights, biomarkers, and therapeutic alternatives for metabolic alterations associated with antipsychotics.

Orexin-A Levels in Relation to the Risk of Metabolic Syndrome in Patients with Schizophrenia Taking Antipsychotics

BACKGROUND

The role of orexin-A in regulating metabolic homeostasis has been recognized, but its association with antipsychotic-induced metabolic abnormalities remains unclear. We investigated the association between orexin-A levels and metabolic syndrome in patients with schizophrenia treated with clozapine or less obesogenic antipsychotics compared with nonpsychiatric controls.

METHODS

Plasma orexin-A levels and metabolic parameters were determined in 159 patients with schizophrenia: 109 taking clozapine; 50 taking aripiprazole, amisulpride, ziprasidone, or haloperidol; and 60 nonpsychiatric controls.

RESULTS

Orexin-A levels were significantly higher in the group taking less obesogenic antipsychotics, followed by the clozapine group and the controls (F=104.6, P<.01). Higher orexin-A levels were correlated with better metabolic profiles in the patient groups but not in the controls. Regression analyses revealed that the patients with higher orexin-A levels had significantly lower risk of metabolic syndrome (adjusted odds ratio [OR]=0.04, 95% CI: 0.01-0.38 for the 2nd tertile; OR=0.04, 95% CI: 0.01-0.36 for the 3rd tertile, compared with the first tertile), after adjustment for age, sex, smoking history, types of antipsychotics (clozapine vs less obesogenic antipsychotics), duration of antipsychotic treatment, and disease severity.

CONCLUSIONS

Our results revealed that the orexin-A level was upregulated in patients with schizophrenia treated with antipsychotics, especially for the group taking less obesogenic antipsychotics. Furthermore, higher orexin-A levels were independently associated with better metabolic profiles. These observations suggest that an upregulation of orexin-A has a protective effect against the development of metabolic abnormalities in patients with schizophrenia receiving antipsychotic treatment.

Symptom dimensions and subgroups in childhood-onset schizophrenia

OBJECTIVE

This study investigated symptom dimensions and subgroups in the National Institute of Mental Health (NIMH) childhood-onset schizophrenia (COS) cohort and their similarities to adult-onset schizophrenia (AOS) literature.

METHOD

Scores from the Scales for the Assessment of Positive and Negative Symptoms (SAPS & SANS) from 125 COS patients were assessed for fit with previously established symptom dimensions from AOS literature using confirmatory factor analysis (CFA). K-means cluster analysis of each individual's scores on the best fitting set of dimensions was used to form patient clusters, which were then compared using demographic and clinical data.

RESULTS

CFA showed the SAPS & SANS data was well suited to a 2-dimension solution, including positive and negative dimensions, out of five well established models. Cluster analysis identified three patient groups characterized by different dimension scores: (1) low scores on both dimensions, (2) high negative, low positive scores, and (3) high scores on both dimensions. These groups had different Full scale IQ, Children's Global Assessment Scale (CGAS) scores, ages of onset, and prevalence of some co-morbid behavior disorders (all p<3.57E-03).

CONCLUSION

Our analysis found distinct symptom-based subgroups within the NIMH COS cohort using an established AOS symptom structure. These findings confirm the heterogeneity of COS and were generally consistent with AOS literature.

Dose-dependent and opposite effects of orexin A on prepulse inhibition response in sleep-deprived and non-sleep-deprived rats

Orexin is a novel neurotransmitter released from lateral hypothalamus, that is a crucial modulator in sleep/wakefulness system. Recent studies also suggest its possible role in the neurodevelopmental disorders, such as schizophrenia. Our study consists of two experiments, where we investigate the effect of orexin A (OXA), one of two isoforms of orexin that can pass blood brain barrier, on the prepulse inhibition of acoustic startle reflex. The first experiment tested the effect of OXA on PPI response of non-sleep-deprived rats via intraperitoneal injection 30min before testing. Our results show that 40μg/kg OXA attenuates PPI% at 78dB and 86dB prepulse intensities. The second experiment utilized 72-h REM sleep deprivation, as a model for sleep-deprivation-induced impairment of PPI response. Here, we tested the effect of OXA on PPI% of sleep-deprived rats via intraperitoneal injection at the last 30min of sleep deprivation, testing for PPI immediately afterwards. Our results showed that (1) sleep deprivation attenuates the PPI% at 74dB, 78dB and 86dB prepulse intensities and (2) 10μg/kg OXA completely restores the impaired PPI% at 78dB only, where the highest PPI% impairment was observed. These results suggest that orexin A modulates PPI response in rats in a dose-dependent manner, oppositely for non-sleep-deprived and sleep-deprived rats, and a more detailed investigation for the etiology of this effect should follow.

Lesions of the paraventricular thalamic nucleus attenuates prepulse inhibition of the acoustic startle reflex

The paraventricular thalamic nucleus (PVT) is a midline nucleus with strong connections to cortical and subcortical brain regions such as the prefrontal cortex, amygdala, nucleus accumbens and hippocampus and receives strong projections from brain stem nuclei. Prepulse inhibition (PPI) is mediated and modulated by complex cortical and subcortical networks that are yet to be fully identified in detail. Here, we suggest that the PVT may be an important brain region for the modulation of PPI. In our study, the paraventricular thalamic nuclei of rats were electrolytically lesioned. Two weeks after the surgery, the PPI responses of the animals were monitored and recorded using measurements of acoustic startle reflex. Our results show that disruption of the PVT dramatically attenuated PPI at prepulse intensities of 74, 78 and 86dB compared to that in the sham lesion group. Thus, we suggest that the PVT may be an important part of the PPI network in the rat brain.

Increased plasma orexin-A levels in patients with insomnia disorder are not associated with prepro-orexin or orexin receptor gene polymorphisms

Orexins, also known as hypocretins, play a regulatory role in the sleep-wake cycle by activating orexin receptors. Previous animal studies have shown that sleep deprivation can elevate orexinergic peptide levels. However, the relationship between insomnia disorder and orexin-A levels in humans has not been explored. In the current study, we examined plasma orexin-A levels in patients with insomnia disorder and in normal sleepers. We also studied the possible mechanisms underlying changes in orexin-A levels between the study groups; this included investigations of prepro-orexin and orexin receptor gene polymorphisms as well as exploration of other variables. We measured plasma orexin-A levels in 228 patients with insomnia disorder and 282 normal sleepers. The results indicated that the patients with insomnia disorder had significantly higher orexin-A levels than normal sleepers (63.42±37.56 vs. 54.84±23.95pg/ml). A positive relationship was detected between orexin-A level and age in patients with insomnia disorder. Orexin-A levels were elevated in relation to course of insomnia, as well as in relation to increased Insomnia Severity Index score. None of the evaluated prepro-orexin gene single nucleotide polymorphisms were informative between the two study populations. After sequencing all orexin receptor exons, one variation (rs2271933) in the OX1R gene and one variation (rs2653349) in the OX2R gene were found. However, no significant differences were found in either genotypic or allelic frequency distributions between the two study groups. It is suggested that the increased plasma orexin-A levels in patients with insomnia disorder are associated with the course and severity of insomnia, but not with prepro-orexin and orexin receptor gene polymorphisms.

The effects of arousal on apical amplification and conscious state

Neocortical pyramidal cells can integrate two classes of input separately and use one to modulate response to the other. Their tuft dendrites are electrotonically separated from basal dendrites and soma by the apical dendrite, and apical hyperpolarization-activated currents (Ih) further isolate subthreshold integration of tuft inputs. When apical depolarization exceeds a threshold, however, it can enhance response to the basal inputs that specify the cell's selective sensitivity. This process is referred to as apical amplification (AA). We review evidence suggesting that, by regulating Ih in the apical compartments, adrenergic arousal controls the coupling between apical and somatic integration zones thus modifying cognitive capabilities closely associated with consciousness. Evidence relating AA to schizophrenia, sleep, and anesthesia is reviewed, and we assess theories that emphasize the relevance of AA to consciousness. Implications for theories of neocortical computation that emphasize context-sensitive modulation are summarized. We conclude that the findings concerning AA and its regulation by arousal offer a new perspective on states of consciousness, the function and evolution of neocortex, and psychopathology. Many issues worthy of closer examination arise.

Diurnal neurobiological alterations after exposure to clozapine in first-episode schizophrenia patients

BACKGROUND

Irregular circadian rhythm and some of its most characteristic symptoms are frequently observed in patients with schizophrenia. However, changes in the expression of clock genes or neuropeptides that are related to the regulation of circadian rhythm may influence the susceptibility to recurrence after antipsychotic treatment in schizophrenia, but this possibility has not been investigated.

METHODS

Blood samples were collected from 15 healthy male controls and 13 male schizophrenia patients at 4h intervals for 24h before and after treatment with clozapine for 8 weeks. The outcome measures included the relative expression of clock gene mRNA PERIOD1 (PER1), PERIOD2 (PER2), PERIOD3 (PER3) and the levels of plasma cortisol, orexin, and insulin.

RESULTS

Compared with healthy controls, schizophrenia patients presented disruptions in diurnal rhythms of the expression of PER1, PER3, and NPAS2 and the release of orexin, accompanied by a delayed phase in the expression of PER2, decreases in PER3 and NPAS2 expression, and an increase in cortisol levels at baseline. Several of these disruptions (i.e., in PER1 and PER3 expression) persisted after 8 weeks of clozapine treatment, similar to the decreases in the 24-h expression of PER3 and NPAS2. Clozapine treatment for 8 weeks significantly decreased the 24-h levels of PER2 and increased the 24-h levels of insulin.

CONCLUSION

These persistent neurobiological changes that occur after 8 weeks of clozapine treatment may contribute to the vulnerability to recurrence and efficacy of long-term maintenance treatment in schizophrenia.

Hypocretins, Neural Systems, Physiology, and Psychiatric Disorders

The hypocretins (Hcrts), also known as orexins, have been among the most intensely studied neuropeptide systems since their discovery about two decades ago. Anatomical evidence shows that the hypothalamic neurons that produce hypocretins/orexins project widely throughout the entire brain, innervating the noradrenergic locus coeruleus, the cholinergic basal forebrain, the dopaminergic ventral tegmental area, the serotonergic raphe nuclei, the histaminergic tuberomammillary nucleus, and many other brain regions. By interacting with other neural systems, the Hcrt system profoundly modulates versatile physiological processes including arousal, food intake, emotion, attention, and reward. Importantly, interruption of the interactions between these systems has the potential to cause neurological and psychiatric diseases. Here, we review the modulation of diverse neural systems by Hcrts and summarize potential therapeutic strategies based on our understanding of the Hcrt system's role in physiology and pathophysiological processes.