Mitochondrial function in individuals at clinical high risk for psychosis

Magnetic Resonance Spectroscopy Studies of Brain Energy Metabolism in Schizophrenia: Progression from Prodrome to Chronic Psychosis

PURPOSE OF REVIEW

Schizophrenia (SZ) is a debilitating mental illness; existing treatments are partially effective and associated with significant side effect burden, largely due to our limited understanding of disease mechanisms and the trajectory of disease progression. Accumulating evidence suggests that metabolic changes associated with glucose metabolism, mitochondrial dysfunction, and redox imbalance play an important role in the pathophysiology of schizophrenia. However, the molecular mechanisms associated with these abnormalities in the brains of schizophrenia patients and the ways in which they change over time remain unclear. This paper aims to review the current literature on molecular mechanisms and in vivo magnetic resonance spectroscopy (MRS) studies of impaired energy metabolism in patients at clinical high risk for psychosis, with first-episode SZ, and with chronic SZ. Our review covers research related to high-energy phosphate metabolism, lactate, intracellular pH, redox ratio, and the antioxidant glutathione.

RECENT FINDINGS

Both first-episode and chronic SZ patients display a significant reduction in creatine kinase reaction activity and redox (NAD + /NADH) ratio in the prefrontal cortex. Chronic, but not first-episode, SZ patients also show a trend toward increased lactate levels and decreased pH value. These findings suggest a progressive shift from oxidative phosphorylation to glycolysis for energy production over the course of SZ, which is associated with redox imbalance and mitochondrial dysfunction. Accumulating evidence indicates that aberrant brain energy metabolism associated with mitochondrial dysfunction and redox imbalance plays a critical role in SZ and will be a promising target for future treatments.

Interaction between peripheral and central immune markers in clinical high risk for psychosis

Neuroinflammatory events prior to the diagnosis of schizophrenia may play a role in transition to illness. To date only one in-vivo study has investigated this association between peripheral proinflammatory cytokines and brain markers of inflammation (e.g., mitochondrial 18 kDa translocator protein, TSPO) in schizophrenia, but none in its putative prodrome. In this study, we primarily aimed to (Barron et al., 2017) test study group (clinical high-risk (CHR) and healthy controls) differences in peripheral inflammatory markers and test for any associations with symptom measures, (Hafizi et al., 2017a) investigate the interaction between brain TSPO levels (dorsolateral prefrontal cortex (DLPFC) and hippocampus) and peripheral inflammatory clusters (entire cohort and (CHR) group independently) within a relatively large group of individuals at CHR for psychosis (N = 38) and healthy controls (N = 20). Participants underwent structural brain magnetic resonance imaging (MRI) and TSPO [18F]FEPPA positron emission tomography (PET) scans. Serum samples were assessed for peripheral inflammatory markers (i.e., CRP and interleukins). For exploratory analysis, we aimed to examine cluster differences for symptom measures and identify independent peripheral predictors of brain TSPO expression. Here, we report increased IL-8 levels that are positively correlated with prodromal general symptom severity and showed trend-level association with apathy in CHR. We identified distinct inflammatory clusters characterized by inflammatory markers (IL-1 β, IL-2, IFN-γ) that were comparable between entire cohort and CHR. TSPO levels did not differ between inflammatory clusters (entire cohort or CHR). Finally, we show that CRP, IL-1 β, TNF-α, and IFN-γ levels were the independent peripheral predictors of brain TSPO expression. Thus, alterations in brain TSPO expression in response to inflammatory processes are not evident in CHR. Taken together, clustering by inflammatory status is a promising strategy to characterize the interaction between brain TSPO and peripheral markers of inflammation.

Defining diurnal fluctuations in mouse choroid plexus and CSF at high molecular, spatial, and temporal resolution

Transmission and secretion of signals via the choroid plexus (ChP) brain barrier can modulate brain states via regulation of cerebrospinal fluid (CSF) composition. Here, we developed a platform to analyze diurnal variations in male mouse ChP and CSF. Ribosome profiling of ChP epithelial cells revealed diurnal translatome differences in metabolic machinery, secreted proteins, and barrier components. Using ChP and CSF metabolomics and blood-CSF barrier analyses, we observed diurnal changes in metabolites and cellular junctions. We then focused on transthyretin (TTR), a diurnally regulated thyroid hormone chaperone secreted by the ChP. Diurnal variation in ChP TTR depended on Bmal1 clock gene expression. We achieved real-time tracking of CSF-TTR in awake TtrmNeonGreen mice via multi-day intracerebroventricular fiber photometry. Diurnal changes in ChP and CSF TTR levels correlated with CSF thyroid hormone levels. These datasets highlight an integrated platform for investigating diurnal control of brain states by the ChP and CSF.

Links of platelet glutamate and glutathione metabolism with attenuated positive and negative symptoms in depressed patients at clinical high risk for psychosis

Aim of the study is to reveal clinical and biological correlations in patients with adolescent depression and attenuated psychotic symptoms. Activity of platelet enzymes involved in glutamate-, glutathione- and energy metabolism was evaluated in control group and in the patients, because these systems are suspected as related to pathogenesis of psychosis. Adolescents (78 men, 16-25 years old) hospitalized with the first acute depressive state composed two groups: with prevalence of attenuated psychotic positive or negative symptoms (Gr1 and Gr2, 48 and 30 patients, respectively). Control group comprised 20 mentally healthy men of 19-25 years old. Gr1 differed significantly from Gr2 in scores by the Scale of Prodromal Symptoms (SOPS) for positive symptoms, p < 0.001, for disorganization symptoms, p < 0.003, and for total SOPS score, p < 0.001, before the treatment started. When patients from either Gr1 or Gr2 were compared with the control group, significantly decreased baseline activities of platelet glutamate dehydrogenase (GDH), glutathione reductase (GR) and glutathione S-transferase (GST) were found (p < 0.0001). Different correlations were found between baseline enzymatic activities in Gr1 and Gr2: GDH activity correlated with GR activity in Gr1 (R = 0.37), and with GST activity in Gr2 (R = 0.70). Significant correlations were found only in Gr2 between the delta of scores by SOPS negative symptoms (SOPS-N) under treatment and baseline GDH, GST, and GR activities (R = - 0.36, R = - 0.60, and R = 0.38, respectively). The found correlations of the baseline enzymatic activity levels with the value of the decrease (delta) in SOPS-N scores under the treatment represent interest for the prediction of the pharmacotherapy efficiency.

Disease-specific differences in gene expression, mitochondrial function and mitochondria-endoplasmic reticulum interactions in iPSC-derived cerebral organoids and cortical neurons in schizophrenia and bipolar disorder

We compared transcriptomic profiles of cerebral organoids differentiated from induced pluripotent stem cells of eight schizophrenia and eight bipolar disorder patients to identify genes that were differentially expressed in cerebral organoids between two disorders. Gene ontology analysis showed relative up-regulation in schizophrenia organoids of genes related to response to cytokines, antigen binding and clathrin-coated vesicles, while showing up-regulation in bipolar disorder of genes involved in calcium binding. Gene set enrichment analysis revealed enrichment in schizophrenia of genes involved in mitochondrial and oxidative phosphorylation while showing enrichment in bipolar disorder of genes involved in long term potentiation and neuro-transporters. We compared mitochondrial function in cerebral organoids from schizophrenia and bipolar disorder subjects and found that while schizophrenia organoids showed deficits in basal oxygen consumption rate and ATP production when compared to healthy control organoids, while bipolar disorder organoids did not show these deficits. Gene ontology analyses also revealed enrichment in bipolar disorder of genes in ion binding and regulation of transport. Experiments examining the interaction between mitochondria and endoplasmic reticulum in cortical neurons from bipolar disorder subjects showed a significantly lower number of contact sites between mitochondria and endoplasmic reticulum when compared to cortical neurons from schizophrenia patients. These results point to disease-specific deficits in mitochondrial respiration in schizophrenia and in mitochondrial-endoplasmic reticulum interactions in bipolar disorder.

Supplementary Information

The online version contains supplementary material available at 10.1007/s44192-023-00031-8.

Serum lipid analysis and isotopic enrichment is suggestive of greater lipogenesis in young long-term cannabis users: A secondary analysis of a case-control study

Cannabis is now legal in many countries and while numerous studies have reported on its impact on cognition and appetite regulation, none have examined fatty acid metabolism in young cannabis users. We conducted an exploratory analysis to evaluate cannabis impact on fatty acid metabolism in cannabis users (n = 21) and non-cannabis users (n = 16). Serum levels of some saturated and monounsaturated fatty acids, including palmitic, palmitoleic, and oleic acids were higher in cannabis users compared to nonusers. As palmitic acid can be derived from diet or lipogenesis from sugars, we evaluated lipogenesis using a de novo lipogenesis index (palmitate/linoleic acid) and carbon-specific isotope analysis, which allows for the determination of fatty acid ¹³ C signature. The significantly higher de novo lipogenesis index in the cannabis users group along with a more enriched ¹³ C signature of palmitic acid suggested an increase in lipogenesis. In addition, while serum glucose concentration did not differ between groups, pyruvate and lactate were lower in the cannabis user group, with pyruvate negatively correlating with palmitic acid. Furthermore, the endocannabinoid 2-arachidonoylglycerol was elevated in cannabis users and could contribute to lipogenesis by activating the cannabinoid receptor 1. Because palmitic acid has been suggested to increase inflammation, we measured peripheral cytokines and observed no changes in inflammatory cytokines. Finally, an anti-inflammatory metabolite of palmitic acid, palmitoylethanolamide was elevated in cannabis users. Our results suggest that lipogenic activity is increased in cannabis users; however, future studies, including prospective studies that control dietary intake are required.

Human studies of mitochondrial biology demonstrate an overall lack of binary sex differences: A multivariate meta-analysis

Mitochondria are maternally inherited organelles that play critical tissue-specific roles, including hormone synthesis and energy production, that influence human development, health, and aging. However, whether mitochondria from women and men exhibit consistent biological differences remains unclear, representing a major gap in knowledge. This meta-analysis systematically examined four domains and six subdomains of mitochondrial biology (total 39 measures), including mitochondrial content, respiratory capacity, reactive oxygen species (ROS) production, morphometry, and mitochondrial DNA copy number. Standardized effect sizes (Hedge's g) of sex differences were computed for each measure using data in 2258 participants (51.5% women) from 50 studies. Only two measures demonstrated aggregate binary sex differences: higher mitochondrial content in women's WAT and isolated leukocyte subpopulations (g = 0.20, χ² p = .01), and higher ROS production in men's skeletal muscle (g = 0.49, χ² p < .0001). Sex differences showed weak to no correlation with age or BMI. Studies with small sample sizes tended to overestimate effect sizes (r = -.17, p < .001), and sex differences varied by tissue examined. Our findings point to a wide variability of findings in the literature concerning possible binary sex differences in mitochondrial biology. Studies specifically designed to capture sex- and gender-related differences in mitochondrial biology are needed, including detailed considerations of physical activity and sex hormones.

Mitochondrial, exosomal miR137-COX6A2 and gamma synchrony as biomarkers of parvalbumin interneurons, psychopathology, and neurocognition in schizophrenia

Early detection and intervention in schizophrenia requires mechanism-based biomarkers that capture neural circuitry dysfunction, allowing better patient stratification, monitoring of disease progression and treatment. In prefrontal cortex and blood of redox dysregulated mice (Gclm-KO ± GBR), oxidative stress induces miR-137 upregulation, leading to decreased COX6A2 and mitophagy markers (NIX, Fundc1, and LC3B) and to accumulation of damaged mitochondria, further exacerbating oxidative stress and parvalbumin interneurons (PVI) impairment. MitoQ, a mitochondria-targeted antioxidant, rescued all these processes. Translating to early psychosis patients (EPP), blood exosomal miR-137 increases and COX6A2 decreases, combined with mitophagy markers alterations, suggest that observations made centrally and peripherally in animal model were reflected in patients' blood. Higher exosomal miR-137 and lower COX6A2 levels were associated with a reduction of ASSR gamma oscillations in EEG. As ASSR requires proper PVI-related networks, alterations in miR-137/COX6A2 plasma exosome levels may represent a proxy marker of PVI cortical microcircuit impairment. EPP can be stratified in two subgroups: (a) a patients' group with mitochondrial dysfunction "Psy-D", having high miR-137 and low COX6A2 levels in exosomes, and (b) a "Psy-ND" subgroup with no/low mitochondrial impairment, including patients having miR-137 and COX6A2 levels in the range of controls. Psy-D patients exhibited more impaired ASSR responses in association with worse psychopathological status, neurocognitive performance, and global and social functioning, suggesting that impairment of PVI mitochondria leads to more severe disease profiles. This stratification would allow, with high selectivity and specificity, the selection of patients for treatments targeting brain mitochondria dysregulation and capture the clinical and functional efficacy of future clinical trials.

The role of mitochondria in the pathophysiology of schizophrenia: A critical review of the evidence focusing on mitochondrial complex one

There has been increasing interest in the role of mitochondrial dysfunction in the pathophysiology of schizophrenia. Mitochondrial complex one (MCI) dysfunction may represent a mechanism linking bioenergetic impairment with the alterations in dopamine signalling, glutamatergic dysfunction, and oxidative stress found in the disorder. New lines of evidence from novel approaches make it timely to review evidence for mitochondrial involvement in schizophrenia, with a specific focus on MCI. The most consistent findings in schizophrenia relative to controls are reductions in expression of MCI subunits in post-mortem brain tissue (Cohen's d> 0.8); reductions in MCI function in post-mortem brains (d> 0.7); and reductions in neural glucose utilisation (d= 0.3 to 0.6). Antipsychotics may affect glucose utilisation, and, at least in vitro, affect MC1. The findings overall are consistent with MCI dysfunction in schizophrenia, but also highlight the need for in vivo studies to determine the link between MCI dysfunction and symptoms in patients. If new imaging tools confirm MCI dysfunction in the disease, this could pave the way for new treatments targeting this enzyme.

Genetically Predicted Brain C4A Expression Is Associated With TSPO and Hippocampal Morphology

BACKGROUND

Alterations in the immune system, particularly C4A, have been implicated in the pathophysiology of schizophrenia. C4A promotes synapse elimination by microglia in preclinical models; however, it is unknown whether this process is also present in living humans and how it affects brain morphology.

METHODS

Participants (N = 111; 33 patients with psychosis, 37 individuals at clinical high risk, and 41 healthy control subjects) underwent a TSPO [¹⁸F]FEPPA positron emission tomography scan and a magnetic resonance imaging scan. Brain C4A expression was genetically predicted as a function of the dosage of each of 4 structural elements (C4AL, C4BL, C4AS, C4BS).

RESULTS

Higher genetically predicted brain C4A expression was associated with higher brain microglial marker (TSPO) and altered hippocampal morphology, including reduced surface area and medial displacement in the CA1 area. This study is the first to quantify genetically predicted brain C4A expression in individuals at clinical high risk, showing significantly lower C4A in individuals at clinical high risk compared with healthy control subjects. We also showed a robust effect of sex on genetically predicted brain C4A expression and effects of both sex and cannabis use on brain TSPO.

CONCLUSIONS

This study shows for the first time complement system (C4A) coupling with a microglial marker (TSPO) and hippocampal morphology in living human brain. These findings pave the way for future research on the interaction between C4A and glial cell function, which has the potential to inform the disease mechanism underlying psychosis and schizophrenia.

Neurobehavioral alterations in a mouse model of chronic partial sleep deprivation

The night shift paradigm induces a state of chronic partial sleep deprivation (CPSD) and enhances the vulnerability to neuronal dysfunction. However, the specific neuronal impact of CPSD has not been thoroughly explored to date. In the current study, the night shift condition was mimicked in female Swiss albino mice. The classical sleep deprivation model, i.e., Modified Multiple Platform (MMP) method, was used for 8 h/day from Monday to Friday with Saturday and Sunday as a weekend off for nine weeks. Following nine weeks of night shift schedule, their neurobehavioral profile and physiological parameters were assessed along with the activity of the mitochondrial complexes, oxidative stress, serotonin levels, and inflammatory markers in the brain. Mice showed an overall hyperactive behavioral profile including hyperlocomotion, aggression, and stereotyped behavior accompanied by decreased activity of mitochondrial enzymes and serotonin levels, increased oxidative stress and inflammatory markers in whole brain homogenates. Collectively, the study points towards the occurrence of a hyperactive behavioral profile akin to mania and psychosis as a potential consequence of CPSD.

A system biology approach based on metabolic biomarkers and protein-protein interactions for identifying pathways underlying schizophrenia and bipolar disorder

Mental disorders (MDs), including schizophrenia (SCZ) and bipolar disorder (BD), have attracted special attention from scientists due to their high prevalence and significantly debilitating clinical features. The diagnosis of MDs is still essentially based on clinical interviews, and intensive efforts to introduce biochemical based diagnostic methods have faced several difficulties for implementation in clinics, due to the complexity and still limited knowledge in MDs. In this context, aiming for improving the knowledge in etiology and pathophysiology, many authors have reported several alterations in metabolites in MDs and other brain diseases. After potentially fishing all metabolite biomarkers reported up to now for SCZ and BD, we investigated here the proteins related to these metabolites in order to construct a protein-protein interaction (PPI) network associated with these diseases. We determined the statistically significant clusters in this PPI network and, based on these clusters, we identified 28 significant pathways for SCZ and BDs that essentially compose three groups representing three major systems, namely stress response, energy and neuron systems. By characterizing new pathways with potential to innovate the diagnosis and treatment of psychiatric diseases, the present data may also contribute to the proposal of new intervention for the treatment of still unmet aspects in MDs.

Antioxidant treatment ameliorates prefrontal hypomyelination and cognitive deficits in a rat model of schizophrenia

Cognitive dysfunction in schizophrenia (SZ) is thought to arise from neurodevelopmental abnormalities that include interneuron hypomyelination in the prefrontal cortex (PFC). Here we report that RNA-sequencing of the medial (m)PFC of the APO-SUS rat model with SZ-relevant cognitive inflexibility revealed antioxidant metabolism as the most-enriched differentially expressed pathway. Antioxidant-related gene expression was altered throughout postnatal development and preceded hypomyelination. Furthermore, reduced glutathione levels and increased mitochondria numbers were observed in the mPFC. Strikingly, chronic treatment with the glutathione precursor N-acetylcysteine (NAC) from postnatal days 5-90 restored not only antioxidant-related mRNA expression and mitochondria numbers, but also myelin-related mRNA expression and mPFC-dependent cognitive dysfunction, while blood glutathione levels remained unaffected. The promyelinating effect of NAC was at least partly due to a positive effect on oligodendrocyte lineage progression. Together, our findings highlight that oxidative stress may contribute to cognitive symptoms in the APO-SUS rat model of SZ and encourage antioxidant therapy in early phases of SZ.

Metabolite Alterations in Adults With Schizophrenia, First Degree Relatives, and Healthy Controls: A Multi-Region 7T MRS Study

Proton magnetic resonance spectroscopy (MRS) studies in schizophrenia have shown altered GABAergic, glutamatergic, and bioenergetic pathways, but if these abnormalities are brain region or illness-stage specific is largely unknown. MRS at 7T MR enables reliable quantification of multiple metabolites, including GABA, glutamate (Glu) and glutamine (Gln), from multiple brain regions within the time constraints of a clinical examination. In this study, GABA, Glu, Gln, the ratio Gln/Glu, and lactate (Lac) were quantified using 7T MRS in five brain regions in adults with schizophrenia (N = 40), first-degree relatives (N = 11), and healthy controls (N = 38). Metabolites were analyzed for differences between groups, as well as between subjects with schizophrenia with either short (<5 years, N = 19 or long (>5 years, N = 21) illness duration. For analyses between the three groups, there were significant glutamatergic and GABAergic differences observed in the anterior cingulate, centrum semiovale, and dorsolateral prefrontal cortex. There were also significant relationships between anterior cingulate cortex, centrum semiovale, and dorsolateral prefrontal cortex and cognitive measures. There were also significant glutamatergic, GABAergic, and lactate differences between subjects with long and short illness duration in the anterior cingulate, centrum semiovale, dorsolateral prefrontal cortex, and hippocampus. Finally, negative symptom severity ratings were significantly correlated with both anterior cingulate and centrum semiovale metabolite levels. In summary, 7T MRS shows multi-region differences in GABAergic and glutamatergic metabolites between subjects with schizophrenia, first-degree relatives and healthy controls, suggesting relatively diffuse involvement that evolves with illness duration. Unmedicated first-degree relatives share some of the same metabolic characteristics as patients with a diagnosis of schizophrenia, suggesting that these differences may reflect a genetic vulnerability and are not solely due to the effects of antipsychotic interventions.

Serum d- and l-lactate, pyruvate and glucose levels in individuals with at-risk mental state and correlations with clinical symptoms

AIM

Little information exists on the peripheral metabolite levels in individuals with at-risk mental state who meet the criteria for a high-risk state of psychosis. Here, we aimed to investigate serum levels of glucose, pyruvate and d- and l-lactate, which may act as a signalling molecule for learning and memory in neuronal cells.

METHODS

High performance liquid chromatography or commercial kits were used to assess serum metabolites in individuals with attenuated psychosis symptoms of at-risk mental state (n = 24, men = 12) who were not receiving antipsychotics. The metabolite levels of these individuals were compared with those of age- and sex-matched healthy individuals (controls, n = 23, men = 11). Correlations between the metabolites and clinical symptoms of at-risk mental state were also examined.

RESULTS

Individuals with at-risk mental state had higher serum glucose levels than did controls (P = 2.18 × 10^-3 ), while no significant difference in pyruvate levels were observed between the groups. Individuals with at-risk mental state had significantly lower serum l-lactate levels than did controls (P = 6.31 × 10^-5 ), while no differences in d-lactate levels were observed. Furthermore, a negative correlation was identified between serum l-lactate levels and Positive and Negative Syndrome Scale negative symptoms scores (r = -0.5651, P = 4.01 × 10^-3 ) in individuals with at-risk mental state.

CONCLUSIONS

We found that, compared with controls, individuals with at-risk mental state have reduced serum l-lactate levels, which may predate psychosis onset, and may be involved in the related negative symptoms.

Role of magnetic resonance spectroscopy in cerebral glutathione quantification for youth mental health: A systematic review

AIM

Oxidative stress is strongly implicated in many psychiatric disorders, which has resulted in the development of new interventions to attempt to perturb this pathology. A great deal of attention has been paid to glutathione, which is the brain's dominant antioxidant and plays a fundamental role in removing free radicals and other reactive oxygen species. Measurement of glutathione concentration in the brain in vivo can provide information on redox status and potential for oxidative stress to develop. Glutathione might also represent a marker to assess treatment response.

METHODS

This paper systematically reviews studies that assess glutathione concentration (measured using magnetic resonance spectroscopy) in various mental health conditions.

RESULTS

There is limited evidence showing altered brain glutathione concentration in mental disorders; the best evidence suggests glutathione is decreased in depression, but is not altered in bipolar disorder. The review then outlines the various methodological options for acquiring glutathione data using spectroscopy.

CONCLUSIONS

Analysis of the minimum effect size measurable in existing studies indicates that increased number of participants is required to measure subtle but possibly important differences and move the field forward.

Alcohol Hangover: Underlying Biochemical, Inflammatory and Neurochemical Mechanisms

AIM

To review current alcohol hangover research in animals and humans and evaluate key evidence for contributing biological factors.

METHOD

Narrative review with alcohol hangover defined as the state the day after a single episode of heavy drinking, when the alcohol concentration in the blood approaches zero.

RESULTS

Many of the human studies of hangover are not well controlled, with subjects consuming different concentrations of alcohol over variable time periods and evaluation not blinded. Also, studies have measured different symptoms and use varying methods of measurement. Animal studies show variations with respect to the route of administration (intragastric or intraperitoneal), the behavioural tests utilised and discrepancy in the timepoint used for hangover onset. Human studies have the advantage over animal models of being able to assess subjective hangover severity and its correlation with specific behaviours and/or biochemical markers. However, animal models provide valuable insight into the neural mechanisms of hangover. Despite such limitations, several hangover models have identified pathological changes which correlate with the hangover state. We review studies examining the contribution of alcohol's metabolites, neurotransmitter changes with particular reference to glutamate, neuroinflammation and ingested congeners to hangover severity.

CONCLUSION

Alcohol metabolites, neurotransmitter alterations, inflammatory factors and mitochondrial dysfunction are the most likely factors in hangover pathology. Future research should aim to investigate the relationship between these factors and their causal role.

Validating mitochondrial electron transport chain content in individuals at clinical high risk for psychosis

Altered mitochondrial electron transport chain function has been implicated in the pathophysiology and etiology of schizophrenia. To date, our previously published study (i.e. first cohort) is still the only study to demonstrate that mitochondrial electron transport chain is not altered in white blood cells from individuals at clinical high risk for psychosis. Here, we aimed to replicate our previous findings with an independent set of samples and validate the levels of mitochondrial complex I-V content in individuals at clinical high risk for psychosis. We demonstrated that the second cohort (i.e. validation cohort) expressed similar results as the first cohort. We combined the first cohort study with the second cohort and once more validated a lack of differential levels in mitochondrial complex I-V content between the two groups. In addition, we were able to validate a correlation between complex III content and prodromal negative symptom severity when the two cohorts studies were combined. Additionally, a correlation between complex V content and prodromal disorganization symptom severity was found when the two cohorts were combined. In conclusion, our results showed that dysfunction of the mitochondrial electron transport chain is not detected in peripheral blood mononuclear cells of individuals in the putative prodromal stage of schizophrenia.

TSPO expression and brain structure in the psychosis spectrum

Psychosis is associated with abnormal structural changes in the brain including decreased regional brain volumes and abnormal brain morphology. However, the underlying causes of these structural abnormalities are less understood. The immune system, including microglial activation, has been implicated in the pathophysiology of psychosis. Although previous studies have suggested a connection between peripheral proinflammatory cytokines and structural brain abnormalities in schizophrenia, no in-vivo studies have investigated whether microglial activation is also linked to brain structure alterations previously observed in schizophrenia and its putative prodrome. In this study, we investigated the link between mitochondrial 18 kDa translocator protein (TSPO) and structural brain characteristics (i.e. regional brain volume, cortical thickness, and hippocampal shape) in key brain regions such as dorsolateral prefrontal cortex and hippocampus of a large group of participants (N = 90) including individuals at clinical high risk (CHR) for psychosis, first-episode psychosis (mostly antipsychotic-naïve) patients, and healthy volunteers. The participants underwent structural brain MRI scan and [¹⁸F]FEPPA positron emission tomography (PET) targeting TSPO. A significant [¹⁸F]FEPPA binding-by-group interaction was observed in morphological measures across the left hippocampus. In first-episode psychosis, we observed associations between [¹⁸F]FEPPA V_T (total volume of distribution) and outward and inward morphological alterations, respectively, in the dorsal and ventro-medial portions of the left hippocampus. These associations were not significant in CHR or healthy volunteers. There was no association between [¹⁸F]FEPPA V_T and other structural brain characteristics. Our findings suggest a link between TSPO expression and alterations in hippocampal morphology in first-episode psychosis.