Interleukin-18 modulation in autism spectrum disorders

Linking specific biological signatures to different childhood adversities: findings from the HERO project

BACKGROUND

Although investigations have begun to differentiate biological and neurobiological responses to a variety of adversities, studies considering both endocrine and immune function in the same datasets are limited.

METHODS

Associations between proximal (family functioning, caregiver depression, and anxiety) and distal (SES-D; socioeconomic disadvantage) early-life adversities with salivary inflammatory biomarkers (IL-1β, IL-6, IL-8, and TNF-α) and hair HPA markers (cortisol, cortisone, and dehydroepiandrosterone) were examined in two samples of young U.S. children (N = 142; N = 145).

RESULTS

Children exposed to higher SES-D had higher levels of TNF-α (B = 0.13, p = 0.011), IL-1β (B = 0.10, p = 0.033), and DHEA (B = 0.16, p = 0.011). Higher family dysfunction was associated with higher cortisol (B = 0.08, p = 0.033) and cortisone (B = 0.05, p = 0.003). An interaction between SES-D and family dysfunction was observed for cortisol levels (p = 0.020) whereby children exposed to lower/average levels of SES-D exhibited a positive association between family dysfunction and cortisol levels, whereas children exposed to high levels of SES-D did not. These findings were partially replicated in the second sample.

CONCLUSIONS

Our results indicate that these biological response systems may react differently to different forms of early-life adversity.

IMPACT

Different forms of early-life adversity have varied stress signatures, and investigations of early-life adversities with inflammation and HPA markers are lacking. Children with higher socioeconomic disadvantage had higher TNF-α, IL-1β, and DHEA. Higher family dysfunction was associated with higher hair cortisol and cortisone levels, and the association between family dysfunction and cortisol was moderated by socioeconomic disadvantage. Biological response systems (immune and endocrine) were differentially associated with distinct forms of early-life adversities.

Olink proteomics profiling platform reveals non-invasive inflammatory related protein biomarkers in autism spectrum disorder

Background

Owing to the lack of valid biomarkers, the diagnosis of autism spectrum disorder (ASD) diagnosis relies solely on the behavioral phenotypes of children. Several researchers have suggested an association between ASD and inflammation; however, the complex relationship between the two is unelucidated to date. Therefore, the current study aims to comprehensively identify novel circulating ASD inflammatory biomarkers.

Methods

Olink proteomics was applied to compare the plasma inflammation-related protein changes in a group of the healthy children (HC, n = 33) and another with ASD (n = 31). The areas under the receiver operating characteristic curves (AUCs) of the differentially expressed proteins (DEPs) were calculated. The functional analysis of the DEPs was performed using Gene Ontology and Kyoto Encyclopedia Genes and Genomes. Pearson correlation tests were used employed to analyze the correlation between the DEPs and clinical features.

Results

A total of 13 DEPs were significantly up-regulated in the ASD group compared with the HC group. The four proteins, namely, STAMBP, ST1A1, SIRT2, and MMP-10 demonstrated good diagnostic accuracy with the corresponding AUCs (95% confidence interval, CI) of 0.7218 (0.5946-0.8489), 0.7107 (0.5827-0.8387), 0.7016 (0.5713-0.8319), and 0.7006 (0.568-0.8332). Each panel of STAMBP and any other differential protein demonstrated a better classification performance [AUC values from 0.7147 (0.5858-0.8436, STAMBP/AXIN1) to 0.7681 (0.6496-0.8867, STAMBP/MMP-10)]. These DEP profiles were enriched in immune and inflammatory response pathways, including TNF and NOD-like receptor signaling pathways. The interaction between STAMBP and SIRT2 (R = 0.97, p = 8.52 × 10^-39) was found to be the most significant. In addition, several DEPs related to clinical features in patients with ASD, particularly AXIN1 (R = 0.36, p = 0.006), SIRT2 (R = 0.34, p = 0.010) and STAMBP (R = 0.34, p = 0.010), were positively correlated with age and parity, indicating that older age and higher parity may be the inflammation-related clinical factors in ASD.

Conclusion

Inflammation plays a crucial role in ASD, and the up-regulated inflammatory proteins may serve as potential early diagnostic biomarkers for ASD.

Systemic inflammatory regulators and 7 major psychiatric disorders: A two-sample Mendelian randomization study

Systemic inflammation has been thought to play a considerable part in psychiatric disorders. However, the causal relationships between systemic inflammation and psychiatric disorders and the directions of the causal effects remain elusive and need further investigation. By leveraging the summary statistics of genome-wide association studies, the standard inverse variance weighted method was applied to assess the causal associations among 41 systemic inflammatory regulators and 7 major psychiatric disorders, including attention-deficit/hyperactivity disorder (ADHD), anorexia nervosa (AN), autism spectrum disorder (ASD), bipolar disorder (BIP), major depression disorder (MDD), obsessive-compulsive disorder (OCD), and schizophrenia (SCZ), within a two-sample bidirectional Mendelian randomization analysis. Additionally, the weighted median test and the Mendelian randomization pleiotropy residual sum and outlier test were conducted for sensitivity analyses. The results suggested a total of 15 unique systemic inflammatory regulators might be causally associated with disease risk, including 2 for ADHD, 4 for AN, 2 for ASD, 2 for MDD, 2 for OCD, and 5 for SCZ. Among them, the genetically predicted concentration of basic fibroblast growth factor was significantly related to AN at the Bonferroni-corrected threshold (Odds ratio = 0.403, 95% confidence interval = (0.261, 0.622), P = 4.03 × 10^-5). Furthermore, the concentrations of 9 systemic inflammatory regulators might be influenced by neuropsychiatric disorders, including 2 by ADHD, 2 by BIP, 3 by MDD, and 2 by SCZ, and the causal effects of ASD, AN, and OCD need to be further assessed when more significant genetic variants are identified in the future. Overall, this study provides additional insights into the relationships between systemic inflammation and psychiatric disorders and may provide new clues regarding the aetiology, diagnosis and treatment of psychiatric disorders.

Food Allergy-Induced Autism-Like Behavior is Associated with Gut Microbiota and Brain mTOR Signaling

Purpose

Food allergy-induced autism-like behavior has been increasing for decades, but the causal drivers of this association are unclear. We sought to test the association of gut microbiota and mammalian/mechanistic target of rapamycin (mTOR) signaling with cow’s milk allergy (CMA)-induced autism pathogenesis.

Methods

Mice were sensitized intragastrically with whey protein containing cholera toxin before sensitization on intraperitoneal injection with whey-containing alum, followed by intragastric allergen challenge to induce experimental CMA. The food allergic immune responses, ASD-like behavioral tests and changes in the mTOR signaling pathway and gut microbial community structure were performed.

Results

CMA mice showed autism-like behavioral abnormalities and several distinct biomarkers. These include increased levels of 5-hydroxymethylcytosine (5-hmC) in the hypothalamus; c-Fos were predominantly located in the region of the lateral orbital prefrontal cortex (PFC), but not ventral; decreased serotonin 1A in amygdala and PFC. CMA mice exhibited a specific microbiota signature characterized by coordinate changes in the abundance of taxa of several bacterial genera, including the Lactobacillus. Interestingly, the changes were accompanied by promoted mTOR signaling in the brain of CMA mice.

Conclusion

We found that disease-associated microbiota and mTOR activation may thus play a pathogenic role in the intestinal, immunological, and psychiatric Autism Spectrum Disorder (ASD)-like symptoms seen in CAM associated autism. However, this is only a preliminary study, and their mechanisms require further investigation.

Neuroinflammation in autism spectrum disorders: Exercise as a "pharmacological" tool

The worldwide prevalence of ASD is around 1%. Although the pathogenesis of ASD is not entirely understood, it is recognized that a combination of genetic, epigenetics, environmental factors and immune system dysfunction can play an essential role in its development. It has been suggested that autism results from the central nervous system derangements due to low-grade chronic inflammatory reactions associated with the immune system activation. ASD individuals have increased microglial activation, density, and increased proinflammatory cytokines in the several brain regions. Autism has no available pharmacological treatments, however there are pedagogical and psychotherapeutic therapies, and pharmacological treatment, that help to control behavioral symptoms. Recent data indicate that exercise intervention programs may improve cognitive and behavioral symptoms in children with ASD. Exercise can also modify inflammatory profiles that will ameliorate associated metabolic disorders. This review highlights the involvement of neuroinflammation in ASD and the beneficial effects of physical exercise on managing ASD symptoms and associated comorbidities.

Long-term behavioral and cell-type-specific molecular effects of early life stress are mediated by H3K79me2 dynamics in medium spiny neurons

Animals susceptible to chronic social defeat stress (CSDS) exhibit depression-related behaviors, with aberrant transcription across several limbic brain regions, most notably in the nucleus accumbens (NAc). Early life stress (ELS) promotes susceptibility to CSDS in adulthood, but associated enduring changes in transcriptional control mechanisms in the NAc have not yet been investigated. In this study, we examined long-lasting changes to histone modifications in the NAc of male and female mice exposed to ELS. Dimethylation of lysine 79 of histone H3 (H3K79me2) and the enzymes (DOT1L and KDM2B) that control this modification are enriched in D2-type medium spiny neurons and are shown to be crucial for the expression of ELS-induced stress susceptibility. We mapped the site-specific regulation of this histone mark genome wide to reveal the transcriptional networks it modulates. Finally, systemic delivery of a small molecule inhibitor of DOT1L reversed ELS-induced behavioral deficits, indicating the clinical relevance of this epigenetic mechanism.

Dual Profile of Environmental Enrichment and Autistic-Like Behaviors in the Maternal Separated Model in Rats

BACKGROUND

Environmental Enrichment (EE) has been suggested as a possible therapeutic intervention for neurodevelopmental disorders such as autism. Although the benefits of this therapeutic method have been reported in some animal models and human studies, the unknown pathophysiology of autism as well as number of conflicting results, urge for further examination of the therapeutic potential of EE in autism. Therefore, the aim of this study was to examine the effects of environmental enrichment on autism-related behaviors which were induced in the maternal separation (MS) animal model.

MATERIAL AND METHODS

Maternally separated (post-natal day (PND) 1-14, 3h/day) and control male rats were at weaning (PND21) age equally divided into rats housed in enriched environment and normal environment. At adolescence (PND42-50), the four groups were behaviorally tested for direct social interaction, sociability, repetitive behaviors, anxiety behavior, and locomotion. Following completion of the behavioral tests, the blood and brain tissue samples were harvested in order to assess plasma level of brain derived neurotrophic factor (BDNF) and structural plasticity of brain using ELISA and stereological methods respectively.

RESULTS

We found that environmental enrichment reduced repetitive behaviors but failed to improve the impaired sociability and anxiety behaviors which were induced by maternal separation. Indeed, EE exacerbated anxiety and social behaviors deficits in association with increased plasma BDNF level, larger volume of the hippocampus and infra-limbic region and higher number of neurons in the infra-limbic area (p < 0.05). Conclusion: We conclude that environmental enrichment has a significant improvement effect on the repetitive behavior as one of the core autistic-like behaviors induced by maternal separation but has negative effect on the anxiety and social behaviors which might have been modulated by BDNF.

Peripheral blood neurotrophic factor levels in children with autism spectrum disorder: a meta-analysis

Increasing evidence suggests that abnormal regulation of neurotrophic factors is involved in the etiology and pathogenesis of Autism Spectrum Disorder (ASD). However, clinical data on neurotrophic factor levels in children with ASD were inconsistent. Therefore, we performed a systematic review of peripheral blood neurotrophic factors levels in children with ASD, and quantitatively summarized the clinical data of peripheral blood neurotrophic factors in ASD children and healthy controls. A systematic search of PubMed and Web of Science identified 31 studies with 2627 ASD children and 4418 healthy controls to be included in the meta-analysis. The results of random effect meta-analysis showed that the peripheral blood levels of brain-derived neurotrophic factor (Hedges’ g = 0.302; 95% CI = 0.014 to 0.591; P = 0.040) , nerve growth factor (Hedges’ g = 0.395; 95% CI = 0.104 to 0.686; P = 0.008) and vascular endothelial growth factor (VEGF) (Hedges’ g = 0.097; 95% CI = 0.018 to 0.175; P = 0.016) in children with ASD were significantly higher than that of healthy controls, whereas blood neurotrophin-3 (Hedges’ g =  − 0.795; 95% CI =  − 1.723 to 0.134; P = 0.093) and neurotrophin-4 (Hedges’ g = 0.182; 95% CI =  − 0.285 to 0.650; P = 0.445) levels did not show significant differences between cases and controls. Taken together, these results clarified circulating neurotrophic factor profile in children with ASD, strengthening clinical evidence of neurotrophic factor aberrations in children with ASD.

Association of Peripheral Blood Levels of Cytokines With Autism Spectrum Disorder: A Meta-Analysis

Background: Although increasing evidence suggests an association between alterations in peripheral cytokines and autism spectrum disorder (ASD), a consensus is lacking. To determine whether abnormal cytokine profiles in peripheral blood were associated with ASD, we performed this systemic review and meta-analysis. Methods: A systematic literature search was conducted through the Embase, PubMed, Web of Knowledge, PsycINFO, and Cochrane databases up to 4 June 2020. Clinical studies exploring the aberration of peripheral cytokines of autistic patients and controls were included in our meta-analysis. We pooled extracted data using fixed- or random-effects models based on heterogeneity tests with Comprehensive Meta-analysis software. We converted standardized mean differences to Hedges' g statistic to obtain the effect sizes adjusted for sample size. Subgroup analyses, sensitivity analyses, meta-regression, and publication bias tests were also carried out. Results: Sixty-one articles (326 studies) were included to assess the association between 76 cytokines and ASD. We conducted our meta-analysis based on 37 cytokines with 289 studies. Since there were fewer than three studies on any of the other 39 cytokines, we only provided basic information for them. The levels of peripheral IL-6, IL-1β, IL-12p70, macrophage migration inhibitory factor (MIF), eotaxin-1, monocyte chemotactic protein-1 (MCP-1), IL-8, IL-7, IL-2, IL-12, tumor necrosis factor-α (TNF-α), IL-17, and IL-4 were defined as abnormal cytokines in the peripheral blood of ASD patients compared with controls. The other 24 cytokines did not obviously change in ASD patients compared with the controls. Conclusions: The findings of our meta-analysis strengthen the evidence for an abnormal cytokine profile in ASD. These abnormal cytokines may be potential biomarkers for the diagnosis and treatment of ASD in the future.

The Role of the Gut Microbiota and the Immune System in the Development of Autism

Autism‌ ‌spectrum‌ ‌disorders‌ ‌(ASDs)‌ ‌are‌ ‌neurodevelopmental‌ ‌disorders‌ ‌that‌ ‌present‌ ‌with‌ ‌social‌ skills‌ ‌and‌ ‌communication‌ ‌challenges,‌ ‌restricted‌ ‌interest,‌ ‌and‌ ‌repetitive‌ ‌behavior.‌ ‌The‌ ‌specific‌ cause ‌of‌ ‌autism‌ ‌is‌ ‌not‌ ‌well‌ ‌understood‌ ‌yet.‌ ‌However,‌ ‌numerous‌ ‌studies‌ ‌indicated‌ ‌that‌ ‌environmental‌ ‌and‌ ‌genetic‌ ‌factors,‌ ‌dysregulated‌ ‌immune‌ ‌response,‌ ‌and‌ ‌alterations‌ ‌to‌ ‌the‌ ‌balance‌ ‌and‌ ‌content‌ ‌of‌ ‌the‌ ‌gut‌ ‌microbiota‌ ‌are‌ ‌implemented‌ ‌in‌ ‌the‌ ‌development‌ ‌of‌ ‌autism.‌ ‌Many‌ ‌non-pharmacological‌ ‌interventions‌ ‌are‌ ‌nominated‌ ‌to‌ ‌manage ‌autism,‌ ‌including‌ ‌family‌ ‌support‌ ‌services‌ ‌and‌ ‌psychoeducational‌ ‌methods‌. Moreover,‌ ‌different‌ ‌pharmacological‌ ‌therapy‌ ‌modalities‌ ‌are‌ ‌recommended‌ ‌for‌ ‌children‌ ‌with‌ ‌ASD.‌ ‌Learning‌ ‌more‌ ‌about‌ ‌the‌ ‌brain,‌ ‌immune‌ ‌system, ‌and‌ ‌gut‌ ‌connections‌ ‌could‌ ‌assist‌ ‌in early‌ ‌diagnosis‌ ‌and‌ ‌treatment‌ ‌of‌ ‌this‌ ‌devastating‌ ‌neurodevelopmental‌ ‌disorders‌ ‌as‌ ‌an‌ ‌early‌ ‌intervention‌ ‌in‌ ‌ASD‌ ‌could‌ ‌improve‌ ‌a‌ ‌child's‌ ‌overall‌ ‌development.‌ We‌ ‌gathered‌ ‌data‌ ‌from‌ ‌relevant‌ ‌previously‌ ‌published‌ ‌articles‌ ‌on‌ ‌PubMed‌ ‌to‌ ‌evaluate ‌the‌ ‌role‌ ‌of‌ ‌the‌ ‌gut‌ ‌microbiota‌ ‌and‌ ‌the‌ ‌immune‌ ‌system‌ ‌on‌ ‌the‌ ‌development‌ ‌of‌ ‌autism.‌.

Microbiota, Immune System and Autism Spectrum Disorders: An Integrative Model towards Novel Treatment Options

BACKGROUND

Autism Spectrum Disorder (ASD) is a condition strongly associated with genetic predisposition and familial aggregation. Among ASD patients, different levels of symptoms severity are detectable, while the presence of intermediate autism phenotypes in close relatives of ASD probands is also known in literature. Recently, increasing attention has been paid to environmental factors that might play a role in modulating the relationship between genomic risk and development and severity of ASD. Within this framework, an increasing body of evidence has stressed a possible role of both gut microbiota and inflammation in the pathophysiology of neurodevelopment. The aim of this paper is to review findings about the link between microbiota dysbiosis, inflammation and ASD.

METHODS

Articles ranging from 1990 to 2018 were identified on PUBMED and Google Scholar databases, with keyword combinations as: microbiota, immune system, inflammation, ASD, autism, broad autism phenotype, adult.

RESULTS

Recent evidence suggests that microbiota alterations, immune system and neurodevelopment may be deeply intertwined, shaping each other during early life. However, results from both animal models and human samples are still heterogeneous, while few studies focused on adult patients and ASD intermediate phenotypes.

CONCLUSION

A better understanding of these pathways, within an integrative framework between central and peripheral systems, might not only shed more light on neural basis of ASD symptoms, clarifying brain pathophysiology, but it may also allow to develop new therapeutic strategies for these disorders, still poorly responsive to available treatments.

Interleukin-18 from neurons and microglia mediates depressive behaviors in mice with post-stroke depression

Post-stroke depression (PSD) is a common and serious complication that is affecting one thirds of stroke patients which leaves them with a poor quality of life, high mortality rate, high recurrent rate, and slow recovery. Recent studies showed that serum interleukin-18 (IL-18) level is a biomarker for patients with PSD. However, the role of IL-18 in the pathology of PSD is still unclear. In this study, we demonstrated that the IL-18 level in the ischemic brain significantly increased in mice with depression-like behaviors that were caused by the combined use of chronic spatial restraint stress and middle cerebral artery occlusion. Interestingly, IL-18 expression was mainly found in neurons at early phase and in microglia at a later phase. Injection of the exogenous IL-18 into the amygdala, but not the hippocampus or the striatum caused severe depression-like behaviors. On the contrary, the blockage of endogenous IL-18 by IL-18 binding protein, a specific antagonist of IL-18, repressed depressive phenotypes in SIR mice. IL-18 KO mice exhibited the resistance to spatial restraint stress and cerebral ischemia injury. Finally, we found that IL-18 mediated depressive behaviors by the interaction of IL-18 receptor and NKCC1, a sodium-potassium chloride co-transporter that is related to GABAergic inhibition. Administration of NKCC1 antagonist bumetanide exerted a therapeutic effect on the in IL-18-induced depressive mice. In conclusion, we demonstrated that increased IL-18 in the brain causes depression-like behaviors by promoting the IL-18 receptor/NKCC1 signaling pathway. Targeting IL-18 and its downstream pathway is a promising strategy for the prevention and treatment of PSD.

Autistic-like behaviours and associated brain structural plasticity are modulated by oxytocin in maternally separated rats

BACKGROUND

Early psycho-social experiences influence the developing brain and possible onset of various neurodevelopmental disorders, such as Autism Spectrum Disorder (ASD). ASD is characterized by a variety of brain abnormalities, including alteration of oxytocin receptors in the brain. Recently, early life adverse experiences, such as maternal separation (MS), have been shown to constitute risk factors for ASD in preclinical studies. Therefore, the main aims of the current study were to i) explore the association between onset of autistic-like behaviours and molecular/structural changes in the brain following MS, and ii) evaluate the possible beneficial effects of oxytocin treatment on the same parameters.

METHOD AND MATERIAL

Male rats were exposed to the maternal separation from post-natal day (PND) 1 to PND14. After weaning, daily injections of oxytocin (1 mg/kg, ip) were administered (PND 22-30), followed by examination of autism-related behaviours at adolescence (PND 42-50). Brain structural plasticity was examined using stereological methods, and the plasma level of brain derived neurotrophic factor (BDNF) was analysed using ELISA.

RESULTS

We found that maternal separation induced autistic-like behaviours, which was associated with increase in the hippocampal CA1 stratum radiatum (CA1.SR) volume. In addition, we observed increase in the infralimbic brain region volume and in the number of the pyramidal neurons in the same brain region. Maternal separation significantly increased the plasma BDNF levels. Treatment with oxytocin improved autistic like behaviours, normalized the number of neurons and the volume of the infralimbic region as well as the plasma BDNF level (p < 0.05).

CONCLUSION

Maternal separation induced autistic-like behaviours, brain structural impairment together with plasma BDNF level abnormality, which could be improved by oxytocin treatment.

Traffic-related particulate matter affects behavior, inflammation, and neural integrity in a developmental rodent model

Recent studies indicate that exposure to airborne particulate matter (PM) is associated with cognitive delay, depression, anxiety, autism, and neurodegenerative diseases; however, the role of PM in the etiology of these outcomes is not well-understood. Therefore, there is a need for controlled animal studies to better elucidate the causes and mechanisms by which PM impacts these health outcomes. We assessed the effects of gestational and early life exposure to traffic-related PM on social- and anxiety-related behaviors, cognition, inflammatory markers, and neural integrity in juvenile male rats. Gestating and lactating rats were exposed to PM from a Boston (MA, USA) traffic tunnel for 5 h/day, 5 days/week for 6 weeks (3 weeks gestation, 3 weeks lactation). The target exposure concentration for the fine fraction of nebulized PM, measured as PM2.5, was 200 μg/m3. To assess anxiety and cognitive function, F1 male juveniles underwent elevated platform, cricket predation, nest building, social behavior and marble burying tests at 32-60 days of age. Upon completion of behavioral testing, multiple cytokines and growth factors were measured in these animals and their brains were analyzed with diffusion tensor MRI to assess neural integrity. PM exposure had no effect on litter size or weight, or offspring growth; however, F1 litters developmentally exposed to PM exhibited significantly increased anxiety (p = 0.04), decreased cognition reflected in poorer nest-organization (p = 0.04), and decreased social play and allogrooming (p = 0.003). MRI analysis of ex vivo brains revealed decreased structural integrity of neural tissues in the anterior cingulate and hippocampus in F1 juveniles exposed to PM (p < 0.01, p = 0.03, respectively). F1 juvenile males exposed to PM also exhibited significantly decreased plasma levels of both IL-18 (p = 0.03) and VEGF (p = 0.04), and these changes were inversely correlated with anxiety-related behavior. Chronic exposure of rat dams and their offspring to traffic-related PM during gestation and lactation decreases social behavior, increases anxiety, impairs cognition, decreases levels of inflammatory and growth factors (which are correlated with behavioral changes), and disrupts neural integrity in the juvenile male offspring. Our findings add evidence that exposure to traffic-related air pollution during gestation and lactation is involved in the etiology of autism spectrum disorder and other disorders which include social and cognitive deficits and/or increased anxiety.

A meta-analysis of pro-inflammatory cytokines in autism spectrum disorders: Effects of age, gender, and latitude

BACKGROUND

Autism spectrum disorders (ASD) occur in 1.5% of the general population worldwide. Studies suggest that ASD might have more costs than diabetes and attention deficit and hyperactivity disorder by 2025. Dysregulation of the cytokine system is well-documented in ASD. We conducted a meta-analysis of studies providing data on circulating concentrations of pro-inflammatory cytokines in people with ASD compared with control subjects without ASD.

METHODS

We identified potentially eligible studies by systematically searching electronic databases from inception to February 2018.

RESULTS

Thirty-eight studies with total of 2487 participants (1393 patients with ASD and 1094 control subjects) were included in the meta-analysis; 13 for interferon (IFN)-γ, 17 for interleukin (IL)-1β, 22 for IL-6, 19 for tumor necrosis factor (TNF)-α, 4 for IL-1α, 6 for IL-2, 4 for IL-7, 8 for IL-8, 14 for IL-12, 3 for IL-15, 12 for IL-17, 3 for IL-18, 3 for IL-2 receptor, 3 for TNF-β, and 3 for IL-23. We found medium increases in levels of plasma IFN-γ (standardized mean difference, SMD = 0.53) and serum IL-1β (SMD = 0.56) and small increases in levels of blood IL-1β (SMD = 0.35), serum IL-6 (SMD = 0.30) and serum TNF-α (SMD = 0.31) for patients with ASD. Meta-regression analyses identified latitude as a negative moderator of the effect size (ES) of difference in mean levels of IFN-γ (R² = 0.26) and TNF-α (R² = 0.74). Also, difference in the mean age between patients and controls had a negative interaction with the ES of difference in mean levels of IL-1β. In contrast, there was a positive effect of the moderator of difference in the proportion of male subjects between patients and controls on the ES of difference in mean levels of IL-1β. We found no significant alterations in peripheral levels of other pro-inflammatory cytokines including IL-1α, IL-2, IL-2R, IL-3, IL-7, IL-8, IL-12, IL-12p40, IL-12p70, IL-15, IL-17, IL-18, IL-23, TBF-β, and TNFRI/II in patients with ASD.

CONCLUSIONS

This meta-analysis provides evidence for higher concentration of pro-inflammatory cytokines IFN-γ, IL-1β, IL-6, and TNF-α in autistic patents compared with control subjects. Also, meta-regression analyses point to the interaction of latitude, age, and gender with peripheral alterations of associated pro-inflammatory cytokines.

The influence of neuroinflammation in Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterised by deficits in social communication and restricted or repetitive behaviours. The clinical presentation of ASD is highly variable and diagnosis is based on the presence of impaired social communication and repetitive and/or restricted behaviours. Although the precise pathophysiologies underlying ASD are unclear, growing evidence supports a role for dysregulated neuroinflammation. The potential involvement of microglia and astrocytes reactive to inflammatory stimuli in ASD has generated much interest due to their varied roles including in mounting an immune response and regulating synaptic function. Increased numbers of reactive microglial and astrocytes in both ASD postmortem tissue and animal models have been reported. Whether dysregulation of glial subtypes exacerbates alterations in neural connectivity in the brain of autistic patients is not well explored. A role for the gut-brain axis involving microbial-immune-neuronal cross talk is also a growing area of neuroinflammation research. Greater understanding of these interactions under patho/physiological conditions and the identification of consistent immune profile abnormalities can potentially lead to more reliable diagnostic measures and treatments in ASD.

Comprehensive literature data-mining analysis reveals a broad genetic network functionally associated with autism spectrum disorder

Previous studies have indicated that genetic factors are the predominate cause of Autism spectrum disorder (ASD). Nevertheless, to the best of our knowledge, to date no systematic study has summarized these data and provided an objective, complete list of genes with demonstrated associations with ASD. The present study included a literature data mining analysis of >2,064 articles including publications from January 2000 to April 2016, which identified 488 ASD target genes. Gene set enrichment analysis (GSEA), sub-network enrichment analysis (SNEA) and network connectivity analysis (NCA) were conducted to assess the functional profile and pathogenic significance of these genes. A total of 2 literature metrics were proposed to prioritize the curated ASD genes with specific significance. This approach resulted in the development of an ASD genetic database. Subsequent analysis indicated that 391 of the 488 genes were enriched in 97 biological pathways (P<1×10⁻⁸), demonstrating significant functional associations with each other. The majority of these curated ASD genes also serve significant roles in the pathogenesis of other neuropsychiatric disorders. These results suggest that the genetic causes of ASD are within a large network composed of functionally-associated genes. The genetic database, together with the metric scores developed in the present study, provides a basis for future biological/genetic modeling in the field.

Zika Virus as a Possible Risk Factor for Autism Spectrum Disorder: Neuroimmunological Aspects

The recent outbreak of the Zika virus (ZIKV) and the discovery that perinatal Zika exposure can lead to the Congenital Zika Syndrome has promoted a call for prevention measures. Due to the increased number of babies born with microcephaly, structural brain abnormalities, and neurological alterations in regions affected by ZIKV, investigations were carried out in order to better understand this process. The maternal immune system directly influences the fetal central nervous system, and complications during pregnancy have been associated with neurodevelopmental disorders. Autism spectrum disorder (ASD), a neurodevelopmental disorder commonly manifested in the first years of life, is a disease with multifactorial etiology and is manifested typically by social and communication impairments, as well as stereotyped behaviors. Brain abnormalities, including both anatomically and functionally, can be observed in this disorder, suggesting delays in neuronal maturation and altered brain connectivity. It is known that some viral congenital infections, such as rubella, and cytomegalovirus can interfere with brain development, being associated with brain calcification, microcephaly, and ASD. Here, we reviewed a range of studies evaluating the aspects concerning brain development, immunological status during pregnancy, and neuroimmunomodulation in congenital viral infections, and we discuss if the fetal brain infection caused by ZIKV could predispose to ASD. Finally, we suggest a mechanism encompassing neurological and immunological pathways that could play a role in the development of ASD in infants after ZIKV infection in pregnancy.