The Role of Cytokines in Predicting the Efficacy of Acute Stage Treatment in Patients with Schizophrenia

Effects of IL-6/IL-6R axis alterations in serum, plasma and cerebrospinal fluid with the schizophrenia: an updated review and meta-analysis of 58 studies

Studies investigating the association between IL-6/IL-6R axis and schizophrenia (SZ) susceptibility found inconsistent data. To reconcile the results, a systematic review followed by a meta-analysis was performed to assess the associations. This study followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. A comprehensive search of the literature was carried out in July 2022 using electronic databases PubMed, EBSCO, Science Direct, PsychInfo, and Scopus. Study quality was assessed by the Newcastle-Ottawa scale. Pooled standard mean difference (SMD) with 95% confidence interval (CI) was calculated by fixed-effect or random-effect model analysis. Fifty-eight studies were identified, including 4,200 SZ patients and 4,531 controls. Our meta-analysis results showed an increase of IL-6 levels in plasma, serum, or CSF and decreased IL-6R levels in serum in patients under treatment. Further studies are needed to better elucidate the correlation between the IL-6/IL-6R axis and the schizophrenia.

The association between peripheral inflammation, brain glutamate and antipsychotic response in Schizophrenia: Data from the STRATA collaboration

Glutamate and increased inflammation have been separately implicated in the pathophysiology of schizophrenia and the extent of clinical response to antipsychotic treatment. Despite the mechanistic links between pro-inflammatory and glutamatergic pathways, the relationships between peripheral inflammatory markers and brain glutamate in schizophrenia have not yet been investigated. In this study, we tested the hypothesis that peripheral levels of pro-inflammatory cytokines would be positively associated with brain glutamate levels in schizophrenia. Secondary analyses determined whether this relationship differed according to antipsychotic treatment response. The sample consisted of 79 patients with schizophrenia, of whom 40 were rated as antipsychotic responders and 39 as antipsychotic non-responders. Brain glutamate levels were assessed in the anterior cingulate cortex (ACC) and caudate using proton magnetic resonance spectroscopy (1H-MRS) and blood samples were collected for cytokine assay on the same study visit (IL-6, IL-8, IL-10, TNF- α and IFN-γ). Across the whole patient sample, there was a positive relationship between interferon-gamma (IFN-γ) and caudate glutamate levels (r = 0.31, p = 0.02). In the antipsychotic non-responsive group only, there was a positive relationship between interleukin-8 (IL-8) and caudate glutamate (r = 0.46, p = 0.01). These findings provide evidence to link specific peripheral inflammatory markers and caudate glutamate in schizophrenia and may suggest that this relationship is most marked in patients who show a poor response to antipsychotic treatment.

Association of Peripheral Inflammatory Biomarkers and Growth Factors Levels with Sex, Therapy and Other Clinical Factors in Schizophrenia and Patient Stratification Based on These Data

Multiple lines of evidence are known to confirm the pro-inflammatory state of some patients with schizophrenia and the involvement of inflammatory mechanisms in the pathogenesis of psychosis. The concentration of peripheral biomarkers is associated with the severity of inflammation and can be used for patient stratification. Here, we analyzed changes in serum concentrations of cytokines (IL-1β, IL-2, IL-4, IL-6, IL-10, IL-21, APRIL, BAFF, PBEF/Visfatin, IFN-α, and TNF-α) and growth/neurotrophic factors (GM-CSF, NRG1-β1, NGF-β, and GDNF) in patients with schizophrenia in an exacerbation phase. IL-1β, IL-2, IL-4, IL-6, BAFF, IFN-α, GM-CSF, NRG1-β1, and GDNF increased but TNF-α and NGF-β decreased in schizophrenia compared to healthy individuals. Subgroup analysis revealed the effect of sex, prevalent symptoms, and type of antipsychotic therapy on biomarker levels. Females, patients with predominantly negative symptoms, and those taking atypical antipsychotics had a more pro-inflammatory phenotype. Using cluster analysis, we classified participants into "high" and "low inflammation" subgroups. However, no differences were found in the clinical data of patients in these subgroups. Nevertheless, more patients (17% to 25.5%) than healthy donors (8.6% to 14.3%) had evidence of a pro-inflammatory condition depending on the clustering approach used. Such patients may benefit from personalized anti-inflammatory therapy.

Longitudinal study of inflammation and relapse in schizophrenia

INTRODUCTION

The clinical course of schizophrenia is often characterized by recurrent relapses. Blood inflammatory markers are altered in acute psychosis, and may be state markers for illness relapse in schizophrenia. Few studies have investigated longitudinal, intra-individual changes in inflammatory markers as a predictor of relapse. In the present study, we explored this association in a relapse prevention trial in patients with schizophrenia.

METHODS

We analyzed blood inflammatory markers in 200 subjects, with a mean 11 samples per subject, during the 30 month Preventing Relapse in schizophrenia: Oral Antipsychotics Compared to Injectable: eValuating Efficacy (PROACTIVE) trial. Associations between longitudinal changes in inflammatory markers and relapse were analyzed using a within-subjects design.

RESULTS

70 (35 %) of subjects relapsed during the study period. There were no significant differences in mean inflammatory marker levels based on relapse status (yes/no). Baseline levels of inflammatory markers did not predict incident relapse. Among subjects who relapsed, there was a significant decrease in mean blood IL-6 (n = 38, p = 0.019) and IFN-γ (n = 44, p = 0.012) levels from the visit before the relapse to the visit after relapse.

CONCLUSION

Although there was some evidence for inflammation as a potential state marker for acute psychosis, we did not find significant evidence for its utility as a relapse-predictive marker.

Acid sphingomyelinase/ceramide system in schizophrenia: implications for therapeutic intervention as a potential novel target

Schizophrenia is a severe mental illness, as the efficacies of current antipsychotic medications are far from satisfactory. An improved understanding of the signaling molecules involved in schizophrenia may provide novel therapeutic targets. Acid sphingomyelinase (ASM) catalyzes cellular membrane sphingomyelin into ceramide, which is further metabolized into sphingosine-1-phophate (S1P). ASM, ceramide, and S1P at the cell surface exert critical roles in the regulation of biophysical processes that include proliferation, apoptosis, and inflammation, and are thereby considered important signaling molecules. Although research on the ASM/ceramide system is still in its infancy, structural and metabolic abnormalities have been demonstrated in schizophrenia. ASM/ceramide system dysfunction is linked to the two important models of schizophrenia, the dopamine (DA) hypothesis through affecting presynaptic DA signaling, and the vulnerability-stress-inflammation model that includes the contribution of stress on the basis of genetic predisposition. In this review, we highlight the current knowledge of ASM/ceramide system dysfunction in schizophrenia gained from human and animal studies, and formulate future directions from the biological landscape for the development of new treatments. Collectively, these discoveries suggest that aberrations in the ASM/ceramide system, especially in ASM activity and levels of ceramide and S1P, may alter cerebral microdomain structure and neuronal metabolism, leading to neurotransmitter (e.g., DA) dysfunction and neuroinflammation. As such, the ASM/ceramide system may offer therapeutic targets for novel medical interventions. Normalization of the aberrant ASM/ceramide system or ceramide reduction by using approved functional inhibitors of ASM, such as fluvoxamine and rosuvastatin, may improve clinical outcomes of patients with schizophrenia. These transformative findings of the ASM/ceramide system in schizophrenia, although intriguing and exciting, may pose scientific questions and challenges that will require further studies for their resolution.

Allostatic load and systemic comorbidities in psychiatric disorders

Psychiatric disorders are complex, disabling, and chronic conditions that are often accompanied by one or more systemic medical comorbidities. In this narrative review, we provide an overview of the allostatic load concept, which represents a multi-system dysregulation in response to chronic stress and link it to systemic comorbidities associated with psychiatric disorders. We synthesized published literature gathered using Medline (Ovid), Scopus, and PsychInfo and identified a high frequency of systemic comorbidities for both mood and psychotic disorders. The identified cardiovascular, metabolic, and immune comorbidities may represent the result of chronic wear and tear caused by a complex interaction between chronic psychosocial stress, health risk behaviors, pharmacological stressors, and the biological systems involved in the development of allostatic load. These findings support the notion that psychiatric disorders should be re-conceptualized as systemic disorders, affecting the brain and systemic biological pathways in an interconnected fashion to result in systemic comorbidities. We suggest that the multi-systemic and multi-dimensional approach that drives the allostatic load concept should be considered for understanding comorbidities in vulnerable psychiatric patients.

Analysis of Gut Microbiota in Patients with Exacerbated Symptoms of Schizophrenia following Therapy with Amisulpride: A Pilot Study

Evidence is mounting that the gut microbiome is related to the underlying pathogenesis of schizophrenia. However, effects of amisulpride on gut microbiota are poorly defined. This study was aimed at analyzing cytokines and fecal microbiota in patients with exacerbated symptoms of schizophrenia treated with amisulpride during four weeks of their hospital stay. In the present study, feces collected from patients with schizophrenia were analyzed using 16S rRNA pyrosequencing and bioinformatic analyses to ascertain gut microbiome composition and fasting peripheral blood cytokines. We found that patients undergoing treatment of schizophrenia with amisulpride had distinct changes in gut microbial composition at the genus level, increased levels of short-chain fatty acid-producing bacteria (Dorea and Butyricicoccus), and reduced levels of pathogenic bacteria (Actinomyces and Porphyromonas), but the level of Desulfovibrio was still high. We also found a significant downregulation of butanoate metabolism based on functional analysis of the microbiome. After treatment, elevated levels of interleukin- (IL-) 4 and decreased levels of IL-6 were found. Our findings extend prior work and suggest a possible pharmacological mechanism of amisulpride treatment for schizophrenia, which acts via mediation of the gut microbiome.

Network Association of Biochemical and Inflammatory Abnormalities With Psychiatric Symptoms in First-Episode Schizophrenia Patients

BACKGROUND

Cardiovascular disease (CVD) risk factors such as dyslipidemia and systemic aberrant inflammatory processes may occur in patients with psychotic disorders, which may cause increased mortality. The interplay between immune and metabolic markers and its contribution to the clinical symptoms of schizophrenia (SCZ) remain unclear. This study aimed to examine the association of a series of inflammatory factors, plasma biochemical indicators, and SCZ clinical symptomatology with the severity of SCZ symptoms.

METHODS

A total of 115 participants, including 79 first-episode drug-naïve patients with SCZ and 36 healthy controls, were enrolled in this study. Semi-structured interviews were used to collect sociodemographic data, family history of SCZ, and medical and psychiatric history. The Brief Psychiatric Rating Scale (BPRS) and the Positive and Negative Syndrome Scale (PANSS) were administered by a clinical psychiatrist to evaluate the symptom severity of patients with SCZ. Plasma inflammatory cytokines were measured by a fully automated electrochemiluminescent immunoassay (Meso Scale Discovery).

RESULTS

Blood routine, biochemical, and inflammation cytokine test results showed that the levels of white blood cell count, neutrophil count, natrium, CRP, IL-8, IL-6, IL-13, and IL-16 significantly increased in the case group than in the healthy controls (p < 0.05), whereas levels of red blood cell count, hemoglobin concentration, mean corpuscular hemoglobin concentration, total protein, albumin, total bile acid, high-density lipoprotein (HDL), apolipoprotein A1, blood urea nitrogen, kalium and IL-15 were lower than in the healthy controls (p < 0.05). Correlation network analysis results shown that the natrium, HDL and red blood cell count were the top 3 factors closely to with BPRS and PANSS related clinical symptoms among of correlation network (degree = 4). ROC curve analysis explored the IL-16, IL-8, IL-13, IL-15, natrium, and HDL had highly sensitivity and specificity to the predictive validity and effectiveness for SCZ symptoms.

CONCLUSION

Our study revealed a complex interactive network correlation among the cardiovascular risk factors, biological immunity profiles, and psychotic symptoms in first-episode patients. Abnormal inflammatory factors and CVD risk factors had high sensitivity and specificity for predicting SCZ symptoms. Generally, our study provided novel information on the immune-related mechanisms involved in early CVD risk in patients with psychotic disorders.

Higher Dietary Inflammation in Patients with Schizophrenia: A Case-Control Study in Korea

Inflammation is a risk factor for the onset and progression of schizophrenia, and dietary factors are related to chronic inflammation. We investigated whether the dietary inflammatory index (DII) is associated with schizophrenia in the Korean population. Of the 256 subjects who responded to the questionnaire, 184 subjects (117 controls; 67 individuals with schizophrenia) were included in this case-control study. A semi-quantitative food frequency questionnaire was used to evaluate the dietary intakes of the study participants. The energy-adjusted DII (E-DII) was used to assess the inflammatory potential of the participants' diets. Dietary intakes of vitamin C, niacin, and folate were significantly reduced in the patients with schizophrenia. The patients with schizophrenia had higher E-DII scores than the controls (p = 0.011). E-DII was positively associated with schizophrenia (odds ratio = 1.254, p = 0.010). The additional analysis confirmed that E-DII was significantly associated with schizophrenia, especially in the third tertile group of E-DII scores (odds ratio = 2.731, p = 0.016). Our findings suggest that patients with schizophrenia have more pro-inflammatory diets.

Role of interleukin 8 in depression and other psychiatric disorders

Low grade neuroinflammation has been suggested as one of the underlying mechanisms of many psychiatric diseases as well as cognitive disorders. Interleukin 8 (IL-8), a proinflammatory cytokine produced by many cell types including macrophage and microglia, mainly functions as a neutrophil chemoattractant in the bloodstream. IL-8 is also found in the brain, where it is released from microglia in response to proinflammatory stimuli. In this review, we highlight studies focusing on the role of IL-8 in psychiatric diseases such as major depression, bipolar disorder, schizophrenia, sleep disorder, autism spectrum disorder, anxiety disorders and dementia. Increased peripheral IL-8 levels have been reported in these diseases, particularly in schizophrenic disorder, bipolar disorder, obstructive sleep apnea and autism spectrum disorder. The literature on IL-8 and major depression is inconsistent. IL-8 has been found to be a factor associated with schizophrenic prognosis and therapeutic response, and may affect a wide range of symptomatology. Considering that the exact role of immune alterations is still under research, the success of immune-based therapies in psychiatric diseases is limited for the time being.

Serum interleukin-6 in schizophrenia: A system review and meta-analysis

BACKGROUND

Schizophrenia is a disabling serious mental illness with unknown etiology. Inflammatory abnormalities play an important role in the pathogenesis of the disease. Many studies had viewed changes in serum IL-6 in schizophrenia, but its results were not consistent. This meta-analysis was to systematically assess the changes in serum IL-6 in schizophrenia.

METHODS

We searched PubMed, Web of Science, ScienceDirect, and EBSCO databases until July 14, 2020, for eligible studies that matched to search subjects, and used Review Manager to counting all the research results.

RESULTS

The meta-analysis included 14 studies comprising 961 schizophrenia and 729 controls. Serum IL-6 was higher in schizophrenia compared with controls (SMD: 0.44 [95%CI: 0.34-0.55] for drug naïve or drug eluted schizophrenia; SMD: 1.55 [95%CI: 0.78-2.31] for schizophrenia after treatment). Serum IL-6 of schizophrenia after treatment was lower than baseline (SMD: 0.33 [95%CI: 0.02-0.63]).

CONCLUSIONS

Serum IL-6 level increase in schizophrenia. It supports the immune regulatory system-compensatory immune regulatory system hypothesis, and the role of inflammatory abnormalities in schizophrenia. And the decrease of serum IL-6 in schizophrenia after treatment suggests that an anti-inflammatory mechanism might be effective during antipsychotic treatment.

The Role of Peripheral Inflammation in Clinical Outcome and Brain Imaging Abnormalities in Psychosis: A Systematic Review

Promising research investigating the association between inflammatory biomarkers and response to antipsychotic and/or adjunctive therapy, observed by improvement in psychiatric assessment, is emerging. Increased inflammation has been suggested to contribute to higher severity of symptoms/treatment resistance through the effects that this has on brain structure and function. The present systematic review aims to clarify the potential role of peripheral inflammatory markers as predictors of clinical outcomes and their association with neuroimaging markers in patients with psychosis. Systematic searches of the literature using the databases PsychInfo, OVID Medline, and Embase were conducted to collate studies investigating the association of inflammatory biomarkers with clinical outcome in patients with psychotic disorders and studies examining the relationships between inflammatory biomarkers and neuroimaging data. Seventeen studies on predictors of clinical outcome and 14 on associations between neuroimaging data and inflammatory biomarkers in psychosis were identified, and risk of bias was assessed using the Newcastle-Ottawa Scale (NOS). The main inflammatory markers associated with clinical outcome in psychosis were interleukin (IL)-6, IL-10, and C-reactive protein (CRP). High levels of CRP and IL-6 were associated with worse clinical outcome and deterioration of symptoms over time; in contrast, increased levels of IL-10 were associated with greater symptoms improvement. Smaller hippocampal volume and reduced cortical thickness were the main neuroimaging markers associated with increased peripheral inflammation. The heterogeneity across the studies (i.e., treatments strategies, duration) suggests that potential prediction power of inflammatory biomarkers could partially depend on the methodologies, supported by the overall NOS ratings of the studies. Future studies may need to consider whether a combination of these inflammatory and neuroimaging markers could further improve our ability of predicting clinical outcome in patients with psychosis.

Evaluating the Hypothesis That Schizophrenia Is an Inflammatory Disorder

The investigation of immune system abnormalities in schizophrenia, although ongoing for decades, has become a popular area of research. The authors present a selected review of studies informing on schizophrenia as a potential inflammatory disorder, emphasizing replicated findings. The authors summarize evidence for inflammation over the illness course, discuss relationships between inflammation and psychopathology, present studies of imaging of neuroinflammation, consider inflammation as a marker of treatment response and treatment target, and review potential mechanisms for the effects of inflammation on the brain in schizophrenia. Although there is not clear and convincing evidence to support the assertion that schizophrenia is an inflammatory disorder, this area of study shows promise toward a greater understanding of the etiopathophysiology of this heterogeneous disorder.

Anti-Inflammatory Diets and Schizophrenia

Schizophrenia is a mental illness characterized by symptoms such as hallucinations, delusions, disorganized speech, disorganized or catatonic behavior, and negative symptoms (emotional flatness, apathy, and lack of speech). It causes social and economic burdens to patients and their family. Although etiology of schizophrenia is still uncertain, dopamine dysregulation is traditionally considered as a main etiological factor of schizophrenia, which has been utilized to develop drugs for treating schizophrenia. Recently, inflammation has presented being a risk factor for schizophrenia in that neuroinflammation contributes to the pathophysiology of schizophrenia and the exacerbation of symptom severity. Various factors including diet can regulate inflammatory state. Specific foods or dietary patterns have anti- or pro-inflammatory potentials. Increased levels of pro-inflammatory cytokines and microglia activation have been reported in schizophrenia populations and were related to the pathogenesis of schizophrenia. Omega-3 fatty acids were often recommended to schizophrenia patients because of their anti-inflammatory activities. In this review, we investigate the inflammation-related pathogenesis of schizophrenia and summarize potential nutritional approaches to inhibit the manifestation of symptoms and to alleviate symptom severity using anti-inflammatory nutrients or functional components.

Longitudinal study of inflammatory markers and psychopathology in schizophrenia

OBJECTIVE

Schizophrenia is associated with abnormal levels of blood inflammatory markers, which may be correlated with levels of psychopathology. Few previous studies have explored whether baseline inflammatory marker levels predict longitudinal changes in psychopathology. In the present study, we explored this association in a cohort of patients with schizophrenia.

METHOD

We investigated inflammatory markers and psychopathology after 3, 6, and 12 months of antipsychotic treatment for subjects with baseline and follow-up data from the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) schizophrenia trial. Linear regression models, controlling for multiple potential confounding factors, were used to investigate these associations.

RESULTS

There was a significant decrease in monocyte, ICAM, and adiponectin levels between baseline and 12 months. Higher baseline blood interleukin-6 (IL-6) predicted greater reduction in PANSS total and general subscale scores at 3 and 6 months, and PANSS negative subscale scores at 3 months (β = -0.10 to -0.16, p < 0.05 for each). Higher baseline blood leptin levels predicted greater reduction in PANSS total, negative and general subscale scores at 6 months (β = -0.09 to -0.11, p < 0.05 for each). In post-hoc analyses, associations between baseline IL-6 levels and symptom reduction were strongest in patients treated with either ziprasidone or quetiapine. Changes in blood inflammatory markers were generally not associated with changes in psychopathology.

CONCLUSIONS

Our findings provide additional support that measuring blood inflammatory markers may be relevant to the clinical care of patients with schizophrenia. Specifically, these markers may help guide selection of antipsychotic treatment towards more personalized medicine approaches for patients with schizophrenia.