Inflammatory disequilibrium and lateral ventricular enlargement in treatment-resistant schizophrenia

Male-biased vulnerability of mouse brain tryptophan/kynurenine and glutamate systems to adolescent exposures to concentrated ambient ultrafine particle air pollution

Air pollution (AP) exposures have been associated with numerous neurodevelopmental and psychiatric disorders, including autism spectrum disorder, attention deficit hyperactivity disorder and schizophrenia, all male-biased disorders with onsets from early life to late adolescence/early adulthood. While prior experimental studies have focused on effects of AP exposures during early brain development, brain development actually extends well into early adulthood. The current study in mice sought to extend the understanding of developmental brain vulnerability during adolescence, a later but significant period of brain development and maturation to the ultrafine particulate (UFPs) component of AP, considered its most reactive component. Additionally, it examined adolescent response to UFPs when preceded by earlier developmental exposures, to ascertain the trajectory of effects and potential enhancement or mitigation of adverse consequences. Outcomes focused on shared features associated with multiple neurodevelopmental disorders. For this purpose, C57Bl/6 J mice of both sexes were exposed to ambient concentrated UFPs or filtered air from PND (postnatal day) 4-7 and PND10-13, and again at PND39-42 and 45-49, resulting in 3 exposure postnatal/adolescent treatment groups per sex: Air/Air, Air/UFP, and UFP/UFP. Features common to neurodevelopmental disorders were examined at PND50. Mass exposure concentration from postnatal exposure averaged 44.34 μg/m3 and the adolescent exposure averaged 49.18 μg/m3. Male brain showed particular vulnerability to UFP exposures in adolescence, with alterations in frontal cortical and striatal glutamatergic and tryptophan/serotonergic neurotransmitters and concurrent reductions in levels of astrocytes in corpus callosum and in serum cytokine levels, with combined exposures resulting in significant reductions in corpus callosum myelination and serum corticosterone. Reductions in serum corticosterone in males correlated with reductions in neurotransmitter levels, and reductions in striatal glutamatergic function specifically correlated with reductions in corpus callosum astrocytes. UFP-induced changes in neurotransmitter levels in males were mitigated by prior postnatal exposure, suggesting potential adaptation, whereas reductions in corticosterone and in corpus callosum neuropathological effects were further strengthened by combined postnatal and adolescent exposures. UFP-induced changes in females occurred primarily in striatal dopamine systems and as reductions in serum cytokines only in response to combined postnatal and adolescent exposures. Findings in males underscore the importance of more integrated physiological assessments of mechanisms of neurotoxicity. Further, these findings provide biological plausibility for an accumulating epidemiologic literature linking air pollution to neurodevelopmental and psychiatric disorders. As such, they support a need for consideration of the regulation of the UFP component of air pollution.

Correlation of Immune-Inflammatory Response System (IRS)/Compensatory Immune-Regulatory Reflex System (CIRS) with White Matter Integrity in First-Episode Patients with Schizophrenia

Several studies have reported compromised white matter integrity, and that some inflammatory mediators may underlie this functional dysconnectivity in the brain of patients with schizophrenia. The immune-inflammatory response system and compensatory immune-regulatory reflex system (IRS/CIRS) are novel biomarkers for exploring the role of immune imbalance in the pathophysiological mechanism of schizophrenia. This study aimed to explore the little-known area regarding the composite score of peripheral cytokines, the IRS/CIRS, and its correlation with white matter integrity and the specific microstructures most affected in schizophrenia. First-episode patients with schizophrenia (FEPS, n = 94) and age- and sex-matched healthy controls (HCs, n = 50) were enrolled in this study. Plasma cytokine levels were measured using enzyme-linked immunosorbent assay (ELISA), and psychopathology was assessed using the Positive and Negative Syndrome Scale (PANSS). The whole brain white matter integrity was measured by fractional anisotropy (FA) from diffusion tensor imaging (DTI) using a 3-T Prisma MRI scanner. The IRS/CIRS in FEPS was significantly higher than that in HCs (p = 1.5 × 10-5) and Cohen's d effect size was d = 0.74. FEPS had a significantly lower whole-brain white matter average FA (p = 0.032), which was negatively associated with IRS/CIRS (p = 0.029, adjusting for age, sex, years of education, BMI, and total intracranial volume), but not in the HCs (p > 0.05). Among the white matter microstructures, only the cortico-spinal tract was significantly correlated with IRS/CIRS in FEPS (r =  - 0.543, p = 0.0009). Therefore, elevated IRS/CIRS may affect the white matter in FEPS.

Role of the immune-kynurenine pathway in treatment-resistant schizophrenia

BACKGROUND

The immune-inflammatory response system (IRS) and kynurenine pathway (KP) have been implicated in the pathophysiology of schizophrenia. Studies have shown inflammation-related effects on KP metabolism in patients with schizophrenia. This study investigated the relationship between KP metabolites, IRS, and the compensatory immune-regulatory reflex system (CIRS) in patients with treatment-resistant schizophrenia (TRS).

METHODS

Patients with (n = 53) and without TRS (n = 47), and healthy controls (HCs, n = 49) were enrolled. We quantified plasma levels of pro-inflammatory cytokines (interleukin [IL]-1β, IL-2, IL-6, soluble(s)IL-6 receptor, IL-8, IL-12, IL-17, IL-18, interferon-γ, and tumor necrosis factor[TNF]-α) and anti-inflammatory cytokines (IL-1 receptor antagonist, IL-4, IL-10, tumor growth factor [TGF]-β1, TGF-β2, soluble (s) IL-2 receptor subunit α, sIL-2 receptor subunit β, and sTNF-α receptor 1) and calculated the IRS/CIRS ratio. We also tested serum metabolites of the KP, including kynurenine (KYN), kynurenic acid (KYNA), and quinolinic acid (QUIN), along with the QUIN/KYNA ratio.

RESULTS

Patients with TRS had significantly higher IRS/CIRS ratio than non-TRS patients (p = 0.002) and HCs (p = 0.007), and significantly lower KYN (p = 0.001) and KYNA (p = 0.01) levels than HCs. Binary logistic regression analysis revealed that a younger age at illness onset (odds ratio [OR] = 0.91, p = 0.02) and a higher IRS/CIRS ratio (OR = 1.22; p = 0.007) were risk factors for patients with TRS. After further adjusted for age of onset, the QUIN/KYNA ratio (β = 0.97; p = 0.02) significantly moderated the relationship between IRS/CIRS and TRS, showing that in the higher QUIN/KYNA condition, higher IRS/CIRS ratio were significantly and more likely to be associated with patients with TRS (β = 0.12, z = 3.19, p = 0.001), whereas in the low QUIN/KYNA condition, the association between IRS/CIRS ratio and TRS was weak and insignificant.

CONCLUSIONS

The peripheral immune response was imbalanced in TRS and was preferentially directed towards the IRS compared to patients without TRS and healthy controls, which is likely to play a role in neurotoxicity. Additionally, peripheral KP activation was also imbalanced, as evidenced by significantly reduced KYN and KYNA levels in patients with TRS compared to healthy controls, but none of KP metabolisms were significantly difference in non-TRS patients compared to healthy controls. QUIN/KYNA ratio involving to the degree of activation of NMDA receptors, indicated the neurotoxic level of the KP activation. The interaction between IRS/CIRS and QUIN/KYNA ratio was significant in predicting TRS, and our findings suggest a potential role for the immune-kynurenine pathway in TRS pathogenesis.

Immune-Inflammatory Response And Compensatory Immune-Regulatory Reflex Systems And White Matter Integrity in Schizophrenia

BACKGROUND AND HYPOTHESIS

Low-grade neural and peripheral inflammation are among the proposed pathophysiological mechanisms of schizophrenia. White matter impairment is one of the more consistent findings in schizophrenia but the underlying mechanism remains obscure. Many cerebral white matter components are sensitive to neuroinflammatory conditions that can result in demyelination, altered oligodendrocyte differentiation, and other changes. We tested the hypothesis that altered immune-inflammatory response system (IRS) and compensatory immune-regulatory reflex system (IRS/CIRS) dynamics are associated with reduced white matter integrity in patients with schizophrenia.

STUDY DESIGN

Patients with schizophrenia (SCZ, 70M/50F, age = 40.76 ± 13.10) and healthy controls (HCs, 38M/27F, age = 37.48 ± 12.31) underwent neuroimaging and plasma collection. A panel of cytokines were assessed using enzyme-linked immunosorbent assay. White matter integrity was measured by fractional anisotropy (FA) from diffusion tensor imaging using a 3-T Prisma MRI scanner. The cytokines were used to generate 3 composite scores: IRS, CIRS, and IRS/CIRS ratio.

STUDY RESULTS

The IRS/CIRS ratio in SCZ was significantly higher than that in HCs (P = .009). SCZ had a significantly lower whole-brain white matter average FA (P < .001), and genu of corpus callosum (GCC) was the most affected white matter tract and its FA was significantly associated with IRS/CIRS (r = 0.29, P = .002). FA of GCC was negatively associated with negative symptom scores in SCZ (r = -0.23, P = .016). There was no mediation effect taking FA of GCC as mediator, for that IRS/CIRS was not associated with negative symptom score significantly (P = .217) in SCZ.

CONCLUSIONS

Elevated IRS/CIRS might partly account for the severity of negative symptoms through targeting the integrity of GCC.

Comprehensive immunoprofiling of neurodevelopmental disorders suggests three distinct classes based on increased neurogenesis, Th-1 polarization or IL-1 signaling

Neurodevelopmental disorders (NDDs) are a spectrum of conditions with commonalities as well as differences in terms of phenome, symptomatome, neuropathology, risk factors and underlying mechanisms. Immune dysregulation has surfaced as a major pathway in NDDs. However, it is not known if neurodevelopmental disorders share a common immunopathogenetic mechanism. In this study, we explored the possibility of a shared immune etiology in three early-onset NDDs, namely Autism Spectrum Disorder (ASD), Attention Deficit Hyperactivity Disorder (ADHD) and Intellectual Disability Disorder (IDD). A panel of 48 immune pathway-related markers was assayed in 135 children with NDDs, represented by 45 children with ASD, ADHD and IDD in each group, along with 35 typically developing children. The plasma levels of 48 immune markers were analyzed on the Multiplex Suspension Assay platform using Pro Human cytokine 48-plex kits. Based on the cytokine/chemokine/growth factor levels, different immune profiles were computed. The primary characteristics of NDDs are depletion of the compensatory immune-regulatory system (CIRS) (z composite of IL-4, IL-10, sIL-1RA, and sIL-2R), increased interleukin (IL)-1 signaling associated with elevated IL-1α and decreased IL-1-receptor antagonist levels, increased neurogenesis, M1/M2 macrophage polarization and increased IL-4 as well as C-C Motif Chemokine Ligand 2 (CCL2) levels. With a cross-validated sensitivity of 81.8% and specificity of 94.4%, these aberrations seem specific for NDDs. Many immunological abnormalities are shared by ASD, ADHD and IDD, which are distinguished by minor differences in IL-9, IL-17 and CCL12. In contrast, machine learning reveals that NDD group consists of three immunologically distinct clusters, with enhanced neurogenesis, Th-1 polarization, or IL-1 signaling as the defining features. NDD is characterized by immune abnormalities that have functional implications for neurogenesis, neurotoxicity, and neurodevelopment. Using machine learning, NDD patients could be classified into subgroups with qualitatively distinct immune disorders that may serve as novel drug targets for the treatment of NDDs.

The association between inflammation and kynurenine pathway metabolites in electroconvulsive therapy for schizophrenia: Implications for clinical efficacy

The kynurenine pathway (KP) of tryptophan has been implicated in the pathogenesis of schizophrenia and its interaction with the immune system has been suggested to play a role. In this study, 28 schizophrenia patients and 25 healthy controls were recruited and divided into different inflammatory subgroups using a two-step recursive clustering analysis. Cytokine gene expression and plasma KP metabolites were measured before, during and after treatment. Our findings indicated that schizophrenia patients had lower levels of Tryptophan (TRP), N-formylkynurenine (NFK), xanthinic acid (XA), quinolinic acid (QA), kynurenic acid (KYNA), KYNA/KYN and QA/KYNA, but higher levels of IL-18 mRNA, KYN/TRP compared to healthy controls (all p < 0.05). After electroconvulsive therapy (ECT), patients with low inflammation achieved better clinical improvement (PANSS scores) compared to those with high inflammation (F = 5.672, P = 0.025), especially in negative symptoms (F = 6.382, P = 0.018, η2 = 0.197). While IL-18 mRNA (F = 32.910, P < 0.0001) was significantly decreased following ECT, the KYN/TRP (F = 3.455, p = 0.047) and KYNA/TRP (F = 4.264, P = 0.026) only significantly decreased in patients with low inflammation. Correlation analyses revealed that baseline IL-18 gene expression significantly correlated with pre- (r = 0.537, p = 0.008) and post-KYNA/TRP (r = 0.443, p = 0.034), post-KYN/TRP (r = 0.510, p = 0.013), and post-negative symptoms (r = 0.525, p = 0.010). Moreover, baseline TRP (r = -0.438, p = 0.037) and XA (r = -0.516, p = 0.012) were negatively correlated with baseline PANSS, while post-KYN (r = -0.475, p = 0.022), 2-AA (r = -0.447, p = 0.032) and KYN/TRP (r = -0.566, p = 0.005) were negatively correlated with Montreal Cognitive Assessment (MoCA) following ECT. Overall, these findings suggested that the association between inflammation and kynurenine pathway plays an essential role in mechanism of ECT for schizophrenia and that the regulation of ECT on KP is influenced by inflammatory characteristics, which may relate to clinical efficacy in schizophrenia.