Engineered Nanoprobes for Immune Activation Monitoring

The activation of the immune system is critical for cancer immunotherapy and treatments of inflammatory diseases. Non-invasive visualization of immunoactivation is designed to monitor the dynamic nature of the immune response and facilitate the assessment of therapeutic outcomes, which, however, remains challenging. Conventional imaging modalities, such as positron emission tomography, computed tomography, etc., were utilized for imaging immune-related biomarkers. To explore the dynamic immune monitoring, probes with signals correlated to biomarkers of immune activation or prognosis are urgently needed. These emerging molecular probes, which turn on the signal only in the presence of the intended biomarker, can improve the detection specificity. These probes with "turn on" signals enable non-invasive, dynamic, and real-time imaging with high sensitivity and efficiency, showing significance for multifunctionality/multimodality imaging. As a result, more and more innovative engineered nanoprobes combined with diverse imaging modalities were developed to assess the activation of the immune system. In this work, we comprehensively review the recent and emerging advances in engineered nanoprobes for monitoring immune activation in cancer or other immune-mediated inflammatory diseases and discuss the potential in predicting the efficacy following treatments. Research on real-time in vivo immunoimaging is still under exploration, and this review can provide guidance and facilitate the development and application of next-generation imaging technologies.

The role of microglia in neuropsychiatric disorders and suicide

This narrative review examines the possible role of microglial cells, first, in neuroinflammation and, second, in schizophrenia, depression, and suicide. Recent research on the interactions between microglia, astrocytes and neurons and their involvement in pathophysiological processes of neuropsychiatric disorders is presented. This review focuses on results from postmortem, positron emission tomography (PET) imaging studies, and animal models of schizophrenia and depression. Third, the effects of antipsychotic and antidepressant drug therapy, and of electroconvulsive therapy on microglial cells are explored and the upcoming development of therapeutic drugs targeting microglia is described. Finally, there is a discussion on the role of microglia in the evolutionary progression of human lineage. This view may contribute to a new understanding of neuropsychiatric disorders.

Applicability, potential and limitations of TSPO PET imaging as a clinical immunopsychiatry biomarker

PURPOSE

TSPO PET imaging may hold promise as a single-step diagnostic work-up for clinical immunopsychiatry. This review paper on the clinical applicability of TSPO PET for primary psychiatric disorders discusses if and why TSPO PET imaging might become the first clinical immunopsychiatry biomarker and the investment prerequisites and scientific advancements needed to accommodate this transition from bench to bedside.

METHODS

We conducted a systematic search of the literature to identify clinical studies of TSPO PET imaging in patients with primary psychiatric disorders. We included both original case-control studies as well as longitudinal cohort studies of patients with a primary psychiatric diagnosis.

RESULTS

Thirty-one original studies met our inclusion criteria. In the field of immunopsychiatry, TSPO PET has until now mostly been studied in schizophrenia and related psychotic disorders, and to a lesser extent in mood disorders and neurodevelopmental disorders. Quantitative TSPO PET appears most promising as a predictive biomarker for the transdiagnostic identification of subgroups or disease stages that could benefit from immunological treatments, or as a prognostic biomarker forecasting patients' illness course. Current scanning protocols are still too unreliable, impractical and invasive for clinical use in symptomatic psychiatric patients.

CONCLUSION

TSPO PET imaging in its present form does not yet offer a sufficiently attractive cost-benefit ratio to become a clinical immunopsychiatry biomarker. Its translation to psychiatric clinical practice will depend on the prioritising of longitudinal research and the establishment of a uniform protocol rendering clinically meaningful TSPO uptake quantification at the shortest possible scan duration without arterial cannulation.

The utility of PET imaging in the diagnosis and management of psychosis: a brief review

Purpose

Advances in the pathophysiological characterization of psychosis has led to a newfound role of biomarkers in diagnostic and prognostic contexts. Further, advances in the accuracy and sensitivity of nuclear medicine imaging techniques, and specifically positron emission tomography (PET), have improved the ability to diagnose and manage individuals experiencing first-episode psychosis or those at greater risk for developing psychosis.

Methods

Literature searches were performed in PubMed, Google Scholar, and Web of Science to identify papers related to the use of PET imaging in the diagnosis or management of psychosis. Search terms used included “positron emission tomography”, “PET imaging”, “psychosis”, “disorders of psychosis”, “schizophrenia”, “biomarkers”, “diagnostic biomarkers”, “prognostic biomarker”, “monitoring biomarker”, “outcome biomarker”, and “predictive biomarker.”

Results

Studies included fell into three categories: those examining microglia, those studying dopamine synthesis capacity, and those examining acetylcholine receptor activity. Microglial imaging has been shown to be ineffective in all patients with psychosis, but some believe it shows promise in a subset of patients with psychosis, although no defining characteristics of said subset have been postulated. Studies of dopamine synthesis capacity suggest that presynaptic dopamine is reliably elevated in patients with psychosis, but levels of dopamine active transporter are not. Further, positron emission tomography (PET) with [18F]fluoro-l-dihydroxyphenylalanine ([18F]FDOPA)-PET has been recently used successfully as a predictive biomarker of dopaminergic treatment response, although more work is needed to validate such findings. Finally, existing studies have also documented lower levels of binding to the α7 nicotinic cholinergic receptor (α7-nAChR) via [18F]-ASEM PET in patients with psychosis, however there is a dearth of prospective, randomized studies evaluating the efficacy of [18F]-ASEM as a diagnostic or monitoring biomarker of any kind.

Conclusion

Molecular imaging has become a useful tool in the diagnosis and management of psychosis. Further work must be done to improve the comparative prognostic value and diagnostic accuracy of different radiotracers.

Brain morphology is differentially impacted by peripheral cytokines in schizophrenia-spectrum disorder

Deficits in brain morphology are one of the most widely replicated neuropathological features in schizophrenia-spectrum disorder (SSD), although their biological underpinnings remain unclear. Despite the existence of hypotheses by which peripheral inflammation may impact brain structure, few studies have examined this relationship in SSD. This study aimed to establish the relationship between peripheral markers of inflammation and brain morphology and determine whether such relationships differed across healthy controls and individuals with first episode psychosis (FEP) and chronic schizophrenia. A panel of 13 pro- and anti-inflammatory cytokines were quantified from serum in 175 participants [n = 84 Healthy Controls (HC), n = 40 FEP, n = 51 Chronic SCZ]. We first performed a series of permutation tests to identify the cytokines most consistently associated with brain structural regions. Using moderation analysis, we then determined the extent to which individual variation in select cytokines, and their interaction with diagnostic status, predicted variation in brain structure. We found significant interactions between cytokine level and diagnosis on brain structure. Diagnostic status significantly moderated the relationship of IFNγ, IL4, IL5 and IL13 with frontal thickness, and of IFNγ and IL5 and total cortical volume. Specifically, frontal thickness was positively associated with IFNγ, IL4, IL5 and IL13 cytokine levels in the healthy control group, whereas pro-inflammatory cytokines IFNγ and IL5 were associated with lower total cortical volume in the FEP group. Our findings suggest that while there were no relationships detected in chronic schizophrenia, the relationship between peripheral inflammatory markers and select brain regions are differentially impacted in FEP and healthy controls. Longitudinal investigations are required to determine whether the relationship between brain structure and peripheral inflammation changes over time.

Personality traits in psychosis and psychosis risk linked to TSPO expression: a neuroimmune marker

Personality has been correlated with differences in cytokine expression, an indicator of peripheral inflammation; however, the associations between personality and central markers of inflammation have never been investigated in vivo in humans. Microglia are the resident macrophages of the central nervous system, and the first responders to tissue damage and brain insult. Microglial activation is associated with elevated expression of translocator protein 18kDa (TSPO), which can be imaged with positron emission tomography (PET) to quantify immune activation in the human brain. This study aimed to investigate the association between personality and TSPO expression across the psychosis spectrum. A total of 61 high-resolution [¹⁸F]FEPPA PET scans were conducted in 28 individuals at clinical high risk (CHR) for psychosis, 19 First-Episode Psychosis (FEP), and 14 healthy volunteers (HVs), and analyzed using a two-tissue compartment model and plasma input function to obtain a total volume of distribution (V_T) as an index of brain TSPO expression (controlling for the rs6971 TSPO polymorphism). Personality was assessed using the Revised NEO Personality Inventory (NEO-PI-R). We found TSPO expression to be specifically associated with neuroticism. A positive association between TSPO expression and neuroticism was found in HVs, in contrast to a nonsignificant, negative association in CHR and significant negative association in FEP. The TSPO-associated neuroticism trait indicates an unexplored connection between neuroimmune activation and personality that varies across the psychosis spectrum.

Perspective: Solving the Heterogeneity Conundrum of TSPO PET Imaging in Psychosis

Positron emission tomography using ligands targeting translocator protein 18 kDa (TSPO PET) is an innovative method to visualize and quantify glial inflammatory responses in the central nervous system in vivo. Compared to some other neuropsychiatric disorders, findings of TSPO PET in schizophrenia and related psychotic disorders have been considerably more heterogeneous. Two conflicting meta-analyses have been published on the topic within the last year: one asserting evidence for decreased TSPO uptake, while the other observed increased TSPO uptake in a selection of studies. In this paper, we review and discuss five hypotheses which may explain the observed variability of TSPO PET findings in psychotic illness, namely that (1) an inflammatory phenotype is only present in a subgroup of psychosis patients; (2) heterogeneity is caused by interference of antipsychotic medication; (3) interference of other clinical confounders in the study populations (such as age, sex, BMI, smoking, and substance use); or (4) methodological variability between studies (such as choice of tracer and kinetic model, genotyping, study power, and diurnal effects); and (5) the glial responses underlying changes in TSPO expression are themselves heterogeneous and dynamic. Finally, we propose four key recommendations for future research proposals to mitigate these different causes of heterogeneity.

Neuroinflammation in schizophrenia: meta-analysis of in vivo microglial imaging studies

BACKGROUND

Converging lines of evidence implicate an important role for the immune system in schizophrenia. Microglia are the resident immune cells of the central nervous system and have many functions including neuroinflammation, axonal guidance and neurotrophic support. We aimed to provide a quantitative review of in vivo PET imaging studies of microglia activation in patients with schizophrenia compared with healthy controls.

METHODS

Demographic, clinical and imaging measures were extracted from each study and meta-analysis was conducted using a random-effects model (Hedge's g). The difference in 18-kDa translocator protein (TSPO) binding between patients with schizophrenia and healthy controls, as quantified by either binding potential (BP) or volume of distribution (VT), was used as the main outcome. Sub-analysis and sensitivity analysis were carried out to investigate the effects of genotype, ligand and illness stage.

RESULTS

In total, 12 studies comprising 190 patients with schizophrenia and 200 healthy controls met inclusion criteria. There was a significant elevation in tracer binding in schizophrenia patients relative to controls when BP was used as an outcome measure, (Hedge's g = 0.31; p = 0.03) but no significant differences when VT was used (Hedge's g = -0.22; p = 0.29).

CONCLUSIONS

In conclusion, there is evidence for moderate elevations in TSPO tracer binding in grey matter relative to other brain tissue in schizophrenia when using BP as an outcome measure, but no difference when VT is the outcome measure. We discuss the relevance of these findings as well as the methodological issues that may underlie the contrasting difference between these outcomes.

Sifting through the surfeit of neuroinflammation tracers

The first phase of molecular brain imaging of microglial activation in neuroinflammatory conditions began some 20 years ago with the introduction of [11C]-( R)-PK11195, the prototype isoquinoline ligand for translocator protein (18 kDa) (TSPO). Investigations by positron emission tomography (PET) revealed microgliosis in numerous brain diseases, despite the rather low specific binding signal imparted by [11C]-( R)-PK11195. There has since been enormous expansion of the repertoire of TSPO tracers, many with higher specific binding, albeit complicated by allelic dependence of the affinity. However, the specificity of TSPO PET for revealing microglial activation not been fully established, and it has been difficult to judge the relative merits of the competing tracers and analysis methods with respect to their sensitivity for detecting microglial activation. We therefore present a systematic comparison of 13 TSPO PET and single photon computed tomography (SPECT) tracers belonging to five structural classes, each of which has been investigated by compartmental analysis in healthy human brain relative to a metabolite-corrected arterial input. We emphasize the need to establish the non-displaceable binding component for each ligand and conclude with five recommendations for a standard approach to define the cellular distribution of TSPO signals, and to characterize the properties of candidate TSPO tracers.

Meta-analysis of Cerebrospinal Fluid Cytokine and Tryptophan Catabolite Alterations in Psychiatric Patients: Comparisons Between Schizophrenia, Bipolar Disorder, and Depression

INTRODUCTION

Schizophrenia, bipolar disorder, and major depressive disorder (MDD) have all been associated with immune system dysfunction, including aberrant cerebrospinal fluid (CSF) levels of cytokines and tryptophan catabolites; however, the pattern of alterations has not been compared across disorders. We performed a meta-analysis of CSF cytokine and tryptophan catabolites in patients with these major psychiatric disorders.

METHODS

Articles were identified by searching Pub Med, PsycInfo, and Web of Science, and the reference lists of these studies.

RESULTS

Twenty-eight studies met the inclusion criteria (16 schizophrenia, 4 bipolar disorder, and 9 MDD). CSF levels of IL-1β and kynurenic acid were significantly increased in patients with schizophrenia and bipolar disorder compared to healthy controls (P < .001). CSF levels of IL-6 and IL-8 were significantly increased in patients with schizophrenia and MDD compared to healthy controls (P ≤ .013).

DISCUSSION

There is preliminary evidence for similarities in the pattern of CSF cytokine and tryptophan catabolite alterations across major psychiatric disorders, although findings must be interpreted with caution in light of small numbers of studies/subjects. Many CSF alterations are also concordant with those in the peripheral blood, particularly for schizophrenia. Findings have important implications for our understanding of the pathophysiology and treatment of major psychiatric disorders.

PET imaging of putative microglial activation in individuals at ultra-high risk for psychosis, recently diagnosed and chronically ill with schizophrenia

We examined putative microglial activation as a function of illness course in schizophrenia. Microglial activity was quantified using [11C](R)-(1-[2-chrorophynyl]-N-methyl-N-[1-methylpropyl]-3 isoquinoline carboxamide (11C-(R)-PK11195) positron emission tomography (PET) in: (i) 10 individuals at ultra-high risk (UHR) of psychosis; (ii) 18 patients recently diagnosed with schizophrenia; (iii) 15 patients chronically ill with schizophrenia; and, (iv) 27 age-matched healthy controls. Regional-binding potential (BPND) was calculated using the simplified reference-tissue model with four alternative reference inputs. The UHR, recent-onset and chronic patient groups were compared to age-matched healthy control groups to examine between-group BPND differences in 6 regions: dorsal frontal, orbital frontal, anterior cingulate, medial temporal, thalamus and insula. Correlation analysis tested for BPND associations with gray matter volume, peripheral cytokines and clinical variables. The null hypothesis of equality in BPND between patients (UHR, recent-onset and chronic) and respective healthy control groups (younger and older) was not rejected for any group comparison or region. Across all subjects, BPND was positively correlated to age in the thalamus (r=0.43, P=0.008, false discovery rate). No correlations with regional gray matter, peripheral cytokine levels or clinical symptoms were detected. We therefore found no evidence of microglial activation in groups of individuals at high risk, recently diagnosed or chronically ill with schizophrenia. While the possibility of 11C-(R)-PK11195-binding differences in certain patient subgroups remains, the patient cohorts in our study, who also displayed normal peripheral cytokine profiles, do not substantiate the assumption of microglial activation in schizophrenia as a regular and defining feature, as measured by 11C-(R)-PK11195 BPND.

Therapeutic efficacy of atypical antipsychotic drugs by targeting multiple stress-related metabolic pathways

Schizophrenia (SZ) is considered to be a multifactorial brain disorder with defects involving many biochemical pathways. Patients with SZ show variable responses to current pharmacological treatments of SZ because of the heterogeneity of this disorder. Stress has a significant role in the pathophysiological pathways and therapeutic responses of SZ. Atypical antipsychotic drugs (AAPDs) can modulate the stress response of the hypothalamic-pituitary-adrenal (HPA) axis and exert therapeutic effects on stress by targeting the prefrontal cortex (PFC) and hippocampus. To evaluate the effects of AAPDs (such as clozapine, risperidone and aripiprazole) on stress, we compared neurochemical profile variations in the PFC and hippocampus between rat models of chronic unpredictable mild stress (CUMS) for HPA axis activation and of long-term dexamethasone exposure (LTDE) for HPA axis inhibition, using an ultraperformance liquid chromatography-mass spectrometry (UPLC-MS/MS)-based metabolomic approach and a multicriteria assessment. We identified a number of stress-induced biomarkers comprising creatine, choline, inosine, hypoxanthine, uric acid, allantoic acid, lysophosphatidylcholines (LysoPCs), phosphatidylethanolamines (PEs), corticosterone and progesterone. Specifically, pathway enrichment and correlation analyses suggested that stress induces oxidative damage by disturbing the creatine-phosphocreatine circuit and purine pathway, leading to excessive membrane breakdown. Moreover, our data suggested that the AAPDs tested partially restore stress-induced deficits by increasing the levels of creatine, progesterone and PEs. Thus, the present findings provide a theoretical basis for the hypothesis that a combined therapy using adenosine triphosphate fuel, antioxidants and omega-3 fatty acids as supplements may have synergistic effects on the therapeutic outcome following AAPD treatment.

The Immune System, Cytokines, and Biomarkers in Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is a pervasive neurodevelopmental condition characterized by variable impairments in communication and social interaction as well as restricted interests and repetitive behaviors. Heterogeneity of presentation is a hallmark. Investigations of immune system problems in ASD, including aberrations in cytokine profiles and signaling, have been increasing in recent times and are the subject of ongoing interest. With the aim of establishing whether cytokines have utility as potential biomarkers that may define a subgroup of ASD, or function as an objective measure of response to treatment, this review summarizes the role of the immune system, discusses the relationship between the immune system, the brain, and behavior, and presents previously-identified immune system abnormalities in ASD, specifically addressing the role of cytokines in these aberrations. The roles and identification of biomarkers are also addressed, particularly with respect to cytokine profiles in ASD.

Towards an Immunophenotype of Schizophrenia: Progress, Potential Mechanisms, and Future Directions

The evidence to date, coupled with advances in immunology and genetics has afforded the field an unparalleled opportunity to investigate the hypothesis that a subset of patients with schizophrenia may manifest an immunophenotype, toward new potential diagnostics and therapeutics to reduce risk, alleviate symptoms, and improve quality of life in both at-risk populations and patients with established schizophrenia. In this paper, we will first summarize the findings on immune dysfunction in schizophrenia, including (1) genetic, prenatal, and premorbid immune risk factors and (2) immune markers across the clinical course of the disorder, including cytokines; C-reactive protein; immune cells; antibodies, autoantibodies and comorbid autoimmune disorders; complement; oxidative stress; imaging of neuroinflammation; infections; and clinical trials of anti-inflammatory agents and immunotherapy. We will then discuss a potential mechanistic framework toward increased understanding of a potential schizophrenia immunophenotype. We will then critically appraise the existing literature, and discuss suggestions for the future research agenda in this area that are needed to rigorously evaluate this hypothesis.

Microglia and Brain Plasticity in Acute Psychosis and Schizophrenia Illness Course: A Meta-Review

OBJECTIVE

Schizophrenia poses a tremendous health, social, and economic burden upon patients and society, indicating current treatment options remain inadequate. Recent findings from several lines of evidence have pointed to the importance of immune system involvement in not only premorbid neurodevelopmental but also subsequent symptom generation and aging processes of brain change in schizophrenia. In this meta-review, we use the summarized evidence from recent quantitative systematic reviews (SRs) and meta-analyses of several subspecialties to critically evaluate the hypothesis that immune-related processes shape the symptomatic presentation and illness course of schizophrenia, both directly and indirectly through altered neuroplasticity.

METHODS

We performed a data search in PubMed for English language SRs and meta-analyses from 2010 to 2017. The methodological quality of the SRs was assessed with the AMSTAR instrument. In addition, we review in this paper 11 original publications on translocator protein (TSPO) positron emission tomography (PET) imaging in schizophrenia.

RESULTS

We reviewed 26 SRs and meta-analyses. Evidence from clinical observational studies of inflammatory or immunological markers and randomized controlled drug trials of immunomodulatory compounds as add-on in the treatment of schizophrenia suggests psychotic exacerbations are accompanied by immunological changes different from those seen in non-acute states, and that the symptoms of schizophrenia can be modified by compounds such as non-steroidal anti-inflammatory drug and minocycline. Information derived from post-mortem brain tissue analysis and PET neuroimaging studies to evaluate microglial activation have added new perspectives to the available evidence, yet these results are very heterogeneous. Each research domain comes with unique opportunities as well as inherent limitations. A better understanding of the (patho-)physiology of microglial cells and their role in neuroplasticity is key to interpreting the immune-related findings in the context of schizophrenia illness exacerbations and progression.

CONCLUSION

Evidence from clinical studies analyzing patients' blood and cerebrospinal fluid samples, neuroimaging and post-mortem brain tissue suggests that aberrant immune responses may define schizophrenia illness' course through altered neuroplasticity representing abnormal aging processes. Most findings are however prone to bias and confounding, and often non-specific to schizophrenia, and a multidisciplinary translational approach is needed to consolidate these findings and link them to other schizophrenia hypotheses.

Microglial activation and progressive brain changes in schizophrenia

Schizophrenia is a debilitating disorder that typically begins in adolescence and is characterized by perceptual abnormalities, delusions, cognitive and behavioural disturbances and functional impairments. While current treatments can be effective, they are often insufficient to alleviate the full range of symptoms. Schizophrenia is associated with structural brain abnormalities including grey and white matter volume loss and impaired connectivity. Recent findings suggest these abnormalities follow a neuroprogressive course in the earliest stages of the illness, which may be associated with episodes of acute relapse. Neuroinflammation has been proposed as a potential mechanism underlying these brain changes, with evidence of increased density and activation of microglia, immune cells resident in the brain, at various stages of the illness. We review evidence for microglial dysfunction in schizophrenia from both neuroimaging and neuropathological data, with a specific focus on studies examining microglial activation in relation to the pathology of grey and white matter. The studies available indicate that the link between microglial dysfunction and brain change in schizophrenia remains an intriguing hypothesis worthy of further examination. Future studies in schizophrenia should: (i) use multimodal imaging to clarify this association by mapping brain changes longitudinally across illness stages in relation to microglial activation; (ii) clarify the nature of microglial dysfunction with markers specific to activation states and phenotypes; (iii) examine the role of microglia and neurons with reference to their overlapping roles in neuroinflammatory pathways; and (iv) examine the impact of novel immunomodulatory treatments on brain structure in schizophrenia.

Paying attention to MMN in schizophrenia

The aim of this review is to explore the phenomenon of reduced mismatch negativity (MMN) in persons with schizophrenia and the possible relationship it has with attention impairments. In doing so we discuss (i) the prediction error account of MMN, (ii) reduced MMN as a faulty predictive processing system in persons with schizophrenia, (iii) the role of these systems in relevance filtering and attentional resource protection, (iv) attentional impairments in persons with schizophrenia, and (v) research that has explored MMN and attention in schizophrenia groups. Our review of the literature suggests that no study has appropriately examined the functional impact of smaller MMN in schizophrenia on the performance of a concurrent attention task. We conclude that future research should explore this notion further in the hope that it might embed MMN findings within outcomes of functional significance to individuals with the illness and those providing treatment. This article is part of a Special Issue entitled SI: Prediction and Attention.

Mismatch negativity (MMN) deficiency: a break-through biomarker in predicting psychosis onset

Currently, the mismatch negativity (MMN) deficit is one of the most robust and replicable findings in schizophrenia, reflecting cognitive and functional decline, psychosocial and socio-occupational impairment, and executive dysfunction in these patients. An important break-through has very recently taken place here in the prediction of conversion to psychosis when the MMN in particular to change in tone duration was recorded in clinically at risk-mental state (ARMS) individuals. Attenuations in the MMN in these patients may be very useful in helping clinicians determine who are most likely to develop a psychotic disorder, as we will review in the present article.

The use of clinical and biological characteristics to predict outcome following First Episode Psychosis

OBJECTIVE

Psychotic illnesses such as schizophrenia and other non-affective psychoses are heterogeneous in disease course and functional outcomes. We review evidence from investigations in clinical psychiatry, neuroimaging, neurocognition, and blood biomarker research suggesting that distinct bio-psycho-social patterns exist at the onset and during the early phase of a First Episode Psychosis (FEP), which can describe the risk of individual illness progression and functional trajectories.

METHOD

A selective literature review was performed on articles drawn from Medline searches for relevant key words. A simulation model was constructed from data derived from two recent publications, selected as examples of studies that investigated multivariate predictors of long-term outcome following FEP.

RESULTS

We illustrate how illness trajectories following FEP could be described based on multimodal sociodemographic, clinical, psychological, and neurobiological information. A clinical modeling simulation shows thatrisk trajectories for achieving long-term favorable or unfavorable outcomes can differ significantly depending on baseline characteristics in combination with MRI and functional measurements within 6 months of disease onset.

CONCLUSIONS

Multimodal trajectory modeling may be useful to describe longitudinal outcomes following FEP. Richlongitudinal data on predictors and outcomes, and better integration of multimodal (sociodemographic, clinical, psychological, biological) data, are required to operationalize this approach. This technique may improve our understanding of course of illness and help to provide a more personalized approach to the assessment and treatment of people presenting with FEP.

The 18 kDa translocator protein, microglia and neuroinflammation

The 18 kDa translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor, is expressed in the injured brain. It has become known as an imaging marker of "neuroinflammation" indicating active disease, and is best interpreted as a nondiagnostic biomarker and disease staging tool that refers to histopathology rather than disease etiology. The therapeutic potential of TSPO as a drug target is mostly based on the understanding that it is an outer mitochondrial membrane protein required for the translocation of cholesterol, which thus regulates the rate of steroid synthesis. This pivotal role together with the evolutionary conservation of TSPO has underpinned the belief that any loss or mutation of TSPO should be associated with significant physiological deficits or be outright incompatible with life. However, against prediction, full Tspo knockout mice are viable and across their lifespan do not show the phenotype expected if cholesterol transport and steroid synthesis were significantly impaired. Thus, the "translocation" function of TSPO remains to be better substantiated. Here, we discuss the literature before and after the introduction of the new nomenclature for TSPO and review some of the newer findings. In light of the controversy surrounding the function of TSPO, we emphasize the continued importance of identifying compounds with confirmed selectivity and suggest that TSPO expression is analyzed within specific disease contexts rather than merely equated with the reified concept of "neuroinflammation."

Towards indicated prevention of psychosis: using probabilistic assessments of transition risk in psychosis prodrome

The concept of indicated prevention has proliferated in psychiatry, and accumulating evidence suggests that it may indeed be possible to prevent or delay the onset of a first episode of psychosis though adequate interventions in individuals deemed at clinical high risk (CHR) for such an event. One challenge undermining these efforts is the relatively poor predictive accuracy of clinical assessments used in practice for CHR individuals, often leading to diagnostic and therapeutic uncertainty reflected in clinical guidelines promoting a 'watch and wait' approach to CHR patients. Using data from published studies, and employing predictive models based on the odds-ratio form of Bayes' rule, we simulated scenarios where clinical interview, neurocognitive testing, structural magnetic resonance imaging and electrophysiology are part of the initial assessment process of a CHR individual (extended diagnostic approach). Our findings indicate that for most at-risk patients, at least three of these assessments are necessary to arrive at a clinically meaningful differentiation into high- intermediate-, and low-risk groups. In particular, patients with equivocal results in the initial assessments require additional diagnostic testing to produce an accurate risk profile forming part of the comprehensive initial assessment. The findings may inform future research into reliable identification and personalized therapeutic targeting of CHR patients, to prevent transition to full-blown psychosis.

Cognitive performance and peripheral endocannabinoid system receptor expression in schizophrenia

Schizophrenia is a chronic psychiatric syndrome characterized by generalized cognitive deficits that are associated with functional impairment. The endocannabinoid system (ECS) modulates neurotransmission and neuronal plasticity and is important for cognitive functioning. Evidence points to the involvement of this neuromodulatory system in the pathophysiology of schizophrenia and that alteration of the ECS on peripheral lymphocytes could reflect central changes. The objective of this study was to compare levels of peripheral endocannabinoid receptor expression in patients with schizophrenia and healthy subjects and find evidence of association between peripheral expression of those receptors and cognitive performance. Patients with stabilized schizophrenia (N=53) and controls (N=22) underwent clinical and cognitive evaluation, and assessment of cannabinoid receptor expression on the surface of peripheral immune cells (lymphocytes, natural killer cells and monocytes) by flow cytometry. Patients with schizophrenia had lower levels of cannabinoid receptor expression on total T lymphocytes, but after controlling for possible confounders this difference did not remain significant. In patients, increased cannabinoid receptor expression on lymphocytes and monocytes was significantly correlated with worst cognitive performance. These data provide additional evidence of the involvement of the ECS in the pathophysiology of cognitive deficits in schizophrenia.

Contributions of experimental psychiatry to research on the psychosis prodrome

In the recent decades, a paradigmatic change in psychosis research and treatment shifted attention toward the early and particularly the prodromal stages of illness. Despite substantial progress with regard to the neuronal underpinnings of psychosis development, the crucial biological mechanisms leading to manifest illness are yet insufficiently understood. Until today, one significant approach to elucidate the neurobiology of psychosis has been the modeling of psychotic symptoms by psychedelic substances in healthy individuals. These models bear the opportunity to evoke particular neuronal aberrations and the respective psychotic symptoms in a controlled experimental setting. In the present paper, we hypothesize that experimental psychiatry bears unique opportunities in elucidating the biological mechanisms of the prodromal stages of psychosis. Psychosis risk symptoms are attenuated, transient, and often only retrospectively reported. The respective neuronal aberrations are thought being dynamic. The correlation of unstable psychopathology with observed neurofunctional disturbances is thus yet largely unclear. In modeling psychosis, the experimental setting allows not only for evoking particular symptoms, but for the concomitant assessment of psychopathology, neurophysiology, and neuropsychology. Herein, the glutamatergic model will be highlighted exemplarily, with special emphasis on its potential contribution to the elucidation of psychosis development. This model of psychosis appears as candidate for modeling the prodrome by inducing psychotic-like symptoms in healthy individuals. Furthermore, it alters pre-attentive processing like the Mismatch Negativity, an electrophysiological component which has recently been identified as a potential predictive marker of psychosis development. In summary, experimental psychiatry bears the potential to further elucidate the biological mechanisms of the psychosis prodrome. A better understanding of the respective pathophysiology might assist in the identification of predictive markers, and the development of preventive treatments.

Future perspectives on the treatment of cognitive deficits and negative symptoms in schizophrenia

Drug discovery based on classic models for cognitive impairment and negative symptoms of schizophrenia have met with only modest success. Because cognitive impairment and negative symptoms may result from disruptions in neurodevelopment, more complex developmental models that integrate environmental and genetic risk factors are needed. In addition, it has become clear that biochemical pathways involved in schizophrenia form complex, interconnected networks. Points at which risk factors converge, such as brain-derived neurotrophic factor (BDNF) and protein kinase B (AKT), and from which processes involved in neuroplasticity diverge, are of particular interest for pharmacologic interventions. This paper reviews elements of neurodevelopmental models for cognitive deficits and negative symptoms of schizophrenia with the aim of identifying potential targets for interventions.

Clinical classification in mental health at the cross-roads: which direction next?

BACKGROUND

After 30 years of consensus-derived diagnostic categories in mental health, it is time to head in new directions. Those categories placed great emphasis on enhanced reliability and the capacity to identify them via standardized checklists. Although this enhanced epidemiology and health services planning, it failed to link broad diagnostic groupings to underlying pathophysiology or specific treatment response.

DISCUSSION

It is time to adopt new goals that prioritize the validation of clinical entities and foster alternative strategies to support those goals. The value of new dimensions (notably clinical staging), that are both clinically relevant and directly related to emerging developmental and neurobiological research, is proposed. A strong emphasis on 'reverse translation' (that is, working back from the clinic to the laboratory) underpins these novel approaches. However, it relies on using diagnostic groupings that already have strong evidence of links to specific risk factors or patterns of treatment response.

SUMMARY

The strategies described abandon the historical divides between clinical neurology, psychiatry and psychology and adopt the promotion of pathways to illness models.

The role of glia in late-life depression

Late-life depression (LLD) has a complex and multifactoral etiology. There is growing interest in elucidating how glia, acting alone or as part of a glial-neuronal network, may contribute to the pathophysiology of depression. In this paper, we explore results from neuroimaging studies showing gray-matter volume loss in key frontal and subcortical structures implicated in LLD, and present the few histological studies that have examined neuronal and glial densities in these regions. Compared to results in younger people with depression, there appear to be age-dependent differences in neuronal pathology but the changes in glial pathology may be more subtle, perhaps reflecting a longer-term compensatory gliosis to earlier damage. We then consider the mechanisms by which both astrocytes and microglia may mediate and modulate neuronal dysfunction and possible degeneration in depression. These include a critical role in the response to peripheral inflammation and central microglial activation, as well as a key role in glutamate metabolism. Advances in our understanding of glia are highlighted, including the role of microglia as "electricians" of the brain and astrocytes as key communicating cells, an integral part of the tripartite synapse. Finally, implications for clinicians are discussed, including the consideration of glia as biomarkers for LLD and incorporation of glia into future therapeutic strategies.

From the prodrome to chronic schizophrenia: the neurobiology underlying psychotic symptoms and cognitive impairments

Schizophrenia is a chronic psychotic disorder that remains a considerable cause of global disease burden. Cognitive impairments are common and contribute significantly to the morbidity of the disorder. Over the last two decades or so molecular imaging studies have refined understanding of the pathophysiology underlying the development of psychosis and cognitive impairments. Firstly they have consistently implicated presynaptic dopaminergic dysfunction in the disorder, finding that dopamine synthesis capacity, dopamine release and baseline dopamine levels are increased in the illness. Secondly recent findings show that dopamine synthesis capacity is elevated in those that go on to develop psychosis in the following year, but not in those that do not, and appears to increase further with the development of psychosis. Thirdly evidence links greater dopamine synthesis capacity to poorer cognitive performance and altered frontal cortical function measured using functional imaging during cognitive tasks. Finally they have provided data on the nature of other neurofunctional alterations in the disorder, in particular in the serotonergic system and neuroinflammation. We review these findings and discuss their implications for understanding the neurobiology of psychosis and cognitive impairments in schizophrenia.

Microglia as modulators of cognition and neuropsychiatric disorders

It has become evident recently only that microglia are not only responsible for immunomodulatory functions in the brain but represent vital components of the larger synaptic formation, which also includes pre and postsynaptic neurones as well as astrocytes. Microglia critically contribute to CNS homeostasis by their actions in phagocytosis of cellular debris, release of a variety of cell signaling factors including neurotrophins and extracellular matrix components and direct contact with neurons. The purpose of this review is to summarize our current understanding of the involvement of microglia in cognitive processes and neuropsychiatric disorders including schizophrenia, bipolar disorder, depression, and Rett syndrome and to outline their potential signaling mechanisms in this context.

Automatic sensory information processing abnormalities across the illness course of schizophrenia

BACKGROUND

Deficits in automatic sensory discrimination, as indexed by a reduction in the mismatch negativity (MMN) and P3a event-related potential amplitudes, are well documented in chronic schizophrenia. However, MMN and P3a have not been sufficiently studied early in the course of psychotic illness. The present study aimed to investigate MMN, P3a and reorienting negativity (RON) across the course of schizophrenia.

METHOD

MMN, P3a, and RON were assessed in 118 subjects across four groups: (1) individuals at risk for psychosis (n=26); (2) recent-onset patients (n=31); (3) chronic patients (n=33); and (4) normal controls (n=28) using a duration-deviant auditory oddball paradigm.

RESULTS

Frontocentral deficits in MMN and P3a were present in all patient groups. The at-risk group's MMN and P3a amplitudes were intermediate to those of the control and recent-onset groups. The recent-onset and chronic patients, but not the at-risk subjects, showed significant RON amplitude reductions, relative to the control group. Associations between MMN, P3a, RON and psychosocial functioning were present in the chronic patients. In the at-risk subjects, P3a and RON deficits were significantly associated with higher levels of negative symptoms.

CONCLUSIONS

Abnormalities in the automatic processes of sensory discrimination, orienting and reorienting of attention are evident in the early phases of schizophrenia and raise the possibility of progressive worsening across stages of the illness. The finding that MMN and P3a, but not RON, were reduced before psychosis onset supports the continued examination of these components as potential early biomarkers of schizophrenia.

The mismatch negativity (MMN)--a unique window to disturbed central auditory processing in ageing and different clinical conditions

In this article, we review clinical research using the mismatch negativity (MMN), a change-detection response of the brain elicited even in the absence of attention or behavioural task. In these studies, the MMN was usually elicited by employing occasional frequency, duration or speech-sound changes in repetitive background stimulation while the patient was reading or watching videos. It was found that in a large number of different neuropsychiatric, neurological and neurodevelopmental disorders, as well as in normal ageing, the MMN amplitude was attenuated and peak latency prolonged. Besides indexing decreased discrimination accuracy, these effects may also reflect, depending on the specific stimulus paradigm used, decreased sensory-memory duration, abnormal perception or attention control or, most importantly, cognitive decline. In fact, MMN deficiency appears to index cognitive decline irrespective of the specific symptomatologies and aetiologies of the different disorders involved.

Mismatch negativity (MMN) reduction in schizophrenia-impaired prediction--error generation, estimation or salience?

The model of mismatch negativity (MMN) as a simple index of change detection has been superseded by a richer understanding of how this event-related potential (ERP) reflects the representation of the sound environment in the brain. Our conceptualization of why the MMN is altered in certain groups must also evolve along with a better understanding of the activities reflected by this component. The detection of change incorporates processes enabling an automatic registration of "sameness", a memory for such regularities and the application of this recent acoustic context to interpreting the present and future state of the environment. It also includes "weighting" the importance of this change to an organism's behaviour. In this light, the MMN has been considered a prediction error signal that occurs when the brain detects that the present state of the world violates a context-driven expectation about the environment. In this paper we revisit the consistent observation of reduced MMN amplitude in patients with schizophrenia. We review existing data to address whether the apparent deficit might reflect problems in prediction error generation, estimation or salience. Possible interpretations of MMN studies in schizophrenia are linked to dominant theories about the neurobiology of the illness.

Impaired MMN/P3a complex in first-episode psychosis: cognitive and psychosocial associations

Mismatch negativity (MMN) is a neurophysiological indicator of the brain's ability to extract relevant information from an irrelevant background. The P3a orienting response often accompanies MMN in deviance detection paradigms. Both MMN and P3a have been described as reliable biomarkers of schizophrenia. MMN/P3a impairments are associated with deficits in verbal memory and attentional switching, reflecting dysfunctions in the temporal and frontal systems, respectively. It remains unresolved whether MMN/P3a are robust biomarkers of psychosis in first-episode patients. Thirty-four young people (18 to 30years) were assessed in this study; 17 first-episode psychosis (FEP) patients were compared to 17 healthy controls. To elicit MMN/P3a, a two-tone passive auditory oddball paradigm with 8% duration deviants was used; event-related potentials were recorded at frontal, central and temporal (mastoid) sites. Neuropsychological assessments included processing speed, attentional switching, simple attention, and verbal learning and memory. Social functioning and quality of life measures were also obtained. The FEP group showed significantly reduced MMN amplitudes compared to controls. The FEP group also showed significantly reduced P3a amplitudes at frontal and central sites compared with controls. As expected, the FEP group also showed significant deficits in attention and verbal learning/memory. Correlational analyses found strong associations between fronto-central MMN/P3a peak amplitude and cognitive/psychosocial functioning. This study provides evidence of early neurobiological markers in young people with FEP. These findings suggest that MMN/P3a impairments are present at early stages of psychosis and that fundamental pre-attentive/deviance detection deficits may mark the beginning of progressive underlying changes with illness onset. Such deficits in FEP appear to have important links with higher-order cognitive and psychosocial functioning.