Brain derived neurotrophic factor (BDNF) and autism spectrum disorders (ASD) in childhood

BDNF and GSK-3beta expression changes underlie the beneficial effects of crocin on behavioral alterations in a rat model of autism induced by prenatal valproic acid administration

Autism spectrum disorder (ASD) is a serious neurodevelopmental disorder characterized by impairments in social interaction, language, and communication and induction of stereotypic behavior. In rodents, prenatal administration of valproic acid (often on 12.5 gestational days) is used for the induction of an ASD-like model. In the present study, we aimed to assess the potential therapeutic effects of crocin (a major component of Saffron, a neuroprotective and anti-inflammatory agent) on behavioral dysfunctions with respect to the level of brain-derived neurotrophic factor (BDNF) and glycogen synthase kinase-3 beta (GSK-3beta) in the medial prefrontal cortex. Valproic acid was intraperitoneally injected at the dose of 600 mg/kg on 12.5 gestational days. BDNF and GSK-3beta expression levels were also measured using real-time PCR. Locomotion, anxiety-like behavior, grooming, and sniffing were also measured in the open-field test. The results showed that prenatal valproic acid administration induced hyperactivity, anxiety-like behavior, increased grooming and sniffing (stereotyped behavior), decreased BDNF levels, and increased GSK-3beta levels in the medial prefrontal cortex. However, crocin dose-dependently restored the effects of prenatal valproic acid administration on behavioral functions and gene expressions. In conclusion, we suggested that BDNF and GSK-3beta expression changes in the medial prefrontal cortex may underlie the pathophysiology of ASD. The therapeutic effects of crocin may be also related to counteracting BDNF and GSK-3beta expression changes induced by prenatal valproic acid.

Probiotics in autism spectrum disorder: Recent insights from animal models

LAY ABSTRACT

Autism spectrum disorder is a neurodevelopmental disorder characterized by a wide range of behavioral alterations, including impaired social interaction and repetitive behaviors. Numerous pharmacological interventions have been developed for autism spectrum disorder, often proving ineffective and accompanied by a multitude of side effects. The gut microbiota is the reservoir of bacteria inhabiting our gastrointestinal tract. The gut microbial alterations observed in individuals with autism spectrum disorder, including elevated levels of Bacteroidetes, Firmicutes, and Proteobacteria, as well as reduced levels of Bifidobacterium, provide a basis for further investigation into the role of the gut microbiota in autism spectrum disorder. Recent preclinical studies have shown favorable outcomes with probiotic therapy, including improvements in oxidative stress, anti-inflammatory effects, regulation of neurotransmitters, and restoration of microbial balance. The aim of this review is to explore the potential of probiotics for the management and treatment of autism spectrum disorder, by investigating insights from recent studies in animals.

Decoding the genetic landscape of autism: A comprehensive review

BACKGROUND

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by heterogeneous symptoms and genetic underpinnings. Recent advancements in genetic and epigenetic research have provided insights into the intricate mechanisms contributing to ASD, influencing both diagnosis and therapeutic strategies.

AIM

To explore the genetic architecture of ASD, elucidate mechanistic insights into genetic mutations, and examine gene-environment interactions.

METHODS

A comprehensive systematic review was conducted, integrating findings from studies on genetic variations, epigenetic mechanisms (such as DNA methylation and histone modifications), and emerging technologies [including Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas9 and single-cell RNA sequencing]. Relevant articles were identified through systematic searches of databases such as PubMed and Google Scholar.

RESULTS

Genetic studies have identified numerous risk genes and mutations associated with ASD, yet many cases remain unexplained by known factors, suggesting undiscovered genetic components. Mechanistic insights into how these genetic mutations impact neural development and brain connectivity are still evolving. Epigenetic modifications, particularly DNA methylation and non-coding RNAs, also play significant roles in ASD pathogenesis. Emerging technologies like CRISPR-Cas9 and advanced bioinformatics are advancing our understanding by enabling precise genetic editing and analysis of complex genomic data.

CONCLUSION

Continued research into the genetic and epigenetic underpinnings of ASD is crucial for developing personalized and effective treatments. Collaborative efforts integrating multidisciplinary expertise and international collaborations are essential to address the complexity of ASD and translate genetic discoveries into clinical practice. Addressing unresolved questions and ethical considerations surrounding genetic research will pave the way for improved diagnostic tools and targeted therapies, ultimately enhancing outcomes for individuals affected by ASD.

Expression Levels of miR -124a, miR-545-3p and BDNF in the Peripheral Blood Mononuclear Cells Are Associated with the Severity of Autism

Background

People with autism frequently exhibit poor social skills, communication difficulties, and repetitive and stereotyped behaviors. MicroRNAs (miRNAs) are potential and promised targets in developing of new treatment strategies for autism. This study aimed to assess the relative expression of miR-124a, miR-34a-3p, miR-545-3p, miR-153, and BDNF in the blood samples of autistic children.

Methods

The children autism rating scale (CARS) was used to determine the severity of autism and to confirm the diagnosis. Blood samples were obtained from 50 patients and 40 age-/sex-matched healthy controls. Expressions of miR-545-3p, miR-34a-3p, miR-124a, and BDNF were evaluated using qRT-PCR. Pearson's correlation coefficient and regression analysis were used to check correlations between relative expressions of the miRNAs and BDNF. Biomarker potencies were assessed by ROC curve analysis.

Results

qRT-PCR analysis showed that the relative expressions of miR-545-3p, miR-34a-3p, miR-124a, and BDNF were significantly higher in the patients' group than the healthy controls. However, the relative expression of miR-153 was significantly lower in the case group than the control group. The relative expression of miR-124a was positively correlated with those of miR-545-3p and BDNF among the patients group. Also, the relative expressions of miR-545-3p and BDNF were positively correlated with each other. The ROC curve data also indicated that miR-124a, miR-34a-3p, miR-545-3p, miR-153, and BDNF could be possible diagnostic biomarker for CARS diagnosis (AUC=0.8328, AUC=0.8354, AUC=0.6727, AUC=0.8518 and AUC=0.8214, respectively).

Conclusions

Deregulation of miR-124a, miR-454-3p and BDNF might be considered as potential biomarkers for severity of autism.

Serum brain-derived neurotrophic factor concentration is different between autism spectrum disorders and intellectual disability children and adolescents

PURPOSE

Recent studies showed that mature brain-derived neurotrophic factor (mBDNF) and its precursor proBDNF are associated with autism spectrum disorders (ASD). Whether their levels are different between ASD and intellectual disability (ID) subjects is not clear. The aim of this study is to compare the serum mBDNF and proBDNF concentration, and mBNDF/proBDNF ratio in ASD and ID volunteers.

METHODS

Children and adolescents with ASD or ID between the ages of 4 and 22 were recruited in Tianjin, China. Serum mBDNF and proBDNF level were tested and Wechsler Preschool and Primary Scale of Intelligence (WPPSI), Wechsler Intelligence Scale for Children (WISC), and Childhood Autism Rating Scale (CARS) evaluations were conducted.

RESULTS

Serum mBDNF concentration and the ratio of mBDNF to proBDNF was higher in ASD subjects than that in ID subjects (P = 0.035 and P < 0.001, respectively), while serum proBDNF of ASD participants was lower compared to that of ID participants (P < 0.001). CARS score was positively correlated with serum mBDNF level (r = 0.33, P = 0.004) and m/p ratio (r = 0.39, P < 0.001), and negatively correlated with serum proBDNF level (r = -0.39, <0.001) after adjusting for age and IQ. The AUC of mBDNF, proBDNF, and m/p ratio were 0.741, 0.790, and 0.854, respectively, after adjusted for age and IQ.

CONCLUSION

Serum mBDNF, proBDNF and m/p ratio were different between ASD and ID group. The three biomarkers displayed good diagnostic values for classification of ASD and ID subjects.

Neurotrophins: Expression of Brain-Lung Axis Development

Neurotrophins (NTs) are a group of soluble growth factors with analogous structures and functions, identified initially as critical mediators of neuronal survival during development. Recently, the relevance of NTs has been confirmed by emerging clinical data showing that impaired NTs levels and functions are involved in the onset of neurological and pulmonary diseases. The alteration in NTs expression at the central and peripheral nervous system has been linked to neurodevelopmental disorders with an early onset and severe clinical manifestations, often named "synaptopathies" because of structural and functional synaptic plasticity abnormalities. NTs appear to be also involved in the physiology and pathophysiology of several airway diseases, neonatal lung diseases, allergic and inflammatory diseases, lung fibrosis, and even lung cancer. Moreover, they have also been detected in other peripheral tissues, including immune cells, epithelium, smooth muscle, fibroblasts, and vascular endothelium. This review aims to provide a comprehensive description of the NTs as important physiological and pathophysiological players in brain and lung development.

Diminished activity-dependent BDNF signaling differentially causes autism-like behavioral deficits in male and female mice

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders with strong genetic heterogeneity and more prevalent in males than females. Recent human genetic studies have identified multiple high-risk genes for ASD, which produce similar phenotypes, indicating that diverse genetic factors converge to common molecular pathways. We and others have hypothesized that activity-dependent neural signaling is a convergent molecular pathway dysregulated in ASD. However, the causal link between diminished activity-dependent neural signaling and ASD remains unclear. Brain-derived neurotrophic factor (BDNF) is a key molecule mediating activity-dependent neural signaling. We therefore hypothesize that diminished activity-dependent BDNF signaling could confer autism-like behavioral deficits. Here, we investigated the effect of diminished activity-dependent BDNF signaling on autism-like behavioral deficits by using mice with genetic knock-in of a human BDNF methionine (Met) allele, which has decreased activity-dependent BDNF release without altering basal BDNF level. Compared with wild-type (WT) controls, diminished activity-dependent BDNF signaling similarly induced anxiety-like behaviors in male and female mice. Notably, diminished activity-dependent BDNF signaling differentially resulted in autism-like social deficits and increased self-grooming in male and female mice, and male mice were more severe than female mice. Again, sexually dimorphic spatial memory deficits were observed in female BDNF^+/Met mice, but not in male BDNF^+/Met mice. Our study not only reveals a causal link between diminished activity-dependent BDNF signaling and ASD-like behavioral deficits, but also identifies previously underappreciated sex-specific effect of diminished activity-dependent BDNF signaling in ASD. These mice with genetic knock-in of the human BDNF Met variant provide a distinct mouse model for studying the cellular and molecular mechanisms underlying diminished activity-dependent neural signaling, the common molecular pathway dysregulated in ASD.

BDNF, proBDNF and IGF-1 serum levels in naïve and medicated subjects with autism

Brain-derived neurotrophic factor (BDNF) and insulin-like growth factor 1 (IGF-1) promote the development and maintenance of neural circuits. Alterations in these factors might contribute to autism spectrum disorder (ASD). We asked whether serum BDNF, proBDNF, and IGF-1 levels are altered in an ASD population compared to controls. We measured serum BDNF, proBDNF, and IGF-1 immunoreactive protein in boys and girls aged 5–15 years old with mild to moderate ASD and non-autistic controls by ELISA. IGF-1 was increased in ASD serum compared to controls and was correlated with age and with CARS scores. Serum BDNF levels did not differ between groups, however, proBDNF serum levels were decreased in subjects with ASD compared to non-autistic controls. Medicated, but not unmedicated, ASD subjects exhibited lower serum proBDNF levels compared to controls, while neither IGF-1 nor BDNF levels differed between treatment groups. These data support the involvement of proBDNF and IGF-1 in the pathogenesis and treatment of autism.

Ketamine administration in early postnatal life as a tool for mimicking Autism Spectrum Disorders core symptoms

Autism Spectrum Disorders (ASD) core symptoms include deficits of social interaction, stereotyped behaviours, dysfunction in language and communication. Beyond them, several additional symptoms, such as cognitive impairment, anxiety-like states and hyperactivity are often occurring, mainly overlapping with other neuropsychiatric diseases. To untangle mechanisms underlying ASD etiology, and to identify possible pharmacological approaches, different factors, such as environmental, immunological and genetic ones, need to be considered. In this context, ASD animal models, aiming to reproduce the wide range of behavioural phenotypes of this uniquely human disorder, represent a very useful tool. Ketamine administration in early postnatal life of mice has already been studied as a suitable animal model resembling psychotic-like symptoms. Here, we investigated whether ketamine administration, at postnatal days 7, 9 and 11, might induce behavioural features able to mimic ASD typical symptoms in adult mice. To this aim, we developed a 4-days behavioural tests battery, including Marble Burying, Hole Board, Olfactory and Social tests, to assess repetitive and stereotyped behaviour, social deficits and anxiety-like symptoms. Moreover, by using this mouse model, we performed neurochemical and biomolecular analyses, quantifying neurotransmitters belonging to excitatory-inhibitory pathways, such as glutamate, glutamine and gamma-aminobutyric acid (GABA), as well as immune activation biomarkers related to ASD, such as CD11b and glial fibrillary acidic protein (GFAP), in the hippocampus and amygdala. Possible alterations in levels of brain-derived neurotrophic factor (BDNF) expression in the hippocampus and amygdala were also evaluated. Our results showed an increase in stereotyped behaviours, together with social impairments and anxiety-like behaviour in adult mice, receiving ketamine administration in early postnatal life. In addition, we found decreased BDNF and enhanced GFAP hippocampal expression levels, accompanied by elevations in glutamate amount, as well as reduction in GABA content in amygdala and hippocampus. In conclusion, early ketamine administration may represent a suitable animal model of ASD, exhibiting face validity to mimic specific ASD symptoms, such as social deficits, repetitive repertoire and anxiety-like behaviour.

Excitatory and Inhibitory Synaptic Imbalance Caused by Brain-Derived Neurotrophic Factor Deficits During Development in a Valproic Acid Mouse Model of Autism

Environmental factors, such as medication during pregnancy, are one of the major causes of autism spectrum disorder (ASD). Valproic acid (VPA) intake during pregnancy has been reported to dramatically elevate autism risk in offspring. Recently, researchers have proposed that VPA exposure could induce excitatory or inhibitory synaptic dysfunction. However, it remains to be determined whether and how alterations in the excitatory/inhibitory (E/I) balance contribute to VPA-induced ASD in a mouse model. In the present study, we explored changes in the E/I balance during different developmental periods in a VPA mouse model. We found that typical markers of pre- and postsynaptic excitatory and inhibitory function involved in E/I balance markedly decreased during development, reflecting difficulties in the development of synaptic plasticity in VPA-exposed mice. The expression of brain-derived neurotrophic factor (BDNF), a neurotrophin that promotes the formation and maturation of glutamatergic and GABAergic synapses during postnatal development, was severely reduced in the VPA-exposed group. Treatment with exogenous BDNF during the critical E/I imbalance period rescued synaptic functions and autism-like behaviors, such as social defects. With these results, we experimentally showed that social dysfunction in the VPA mouse model of autism might be caused by E/I imbalance stemming from BDNF deficits during the developmental stage.

Altered Cytokine and BDNF Levels in Individuals with Autism Spectrum Disorders

Previous studies have shown that immunological factors are involved in the pathogenesis of autism spectrum disorders (ASDs). The present study examined whether immunological abnormalities are associated with cognitive and behavioral deficits in children with ASD and whether children with ASD show different immunological biomarkers and brain-derived neurotrophic factor BDNF levels than typically developing (TD) children. Sixteen children with TD and 18 children with ASD, aged 6–18 years, voluntarily participated in the study. Participants’ executive functions were measured using neuropsychological tests, and behavioral measures were measured using parent ratings. Immunological measures were assessed by measuring the participants’ blood serum levels of chemokine ligand 2 (CCL2) and chemokine ligand 5 (CCL5). Children with ASD showed greater deficits in cognitive functions as well as altered levels of immunological measures when compared to TD children, and their cognitive functions and behavioral deficits were significantly associated with increased CCL5 levels and decreased BDNF levels. These results provide evidence to support the notion that altered immune functions and neurotrophin deficiency are involved in the pathogenesis of ASD.

Paracetamol (Acetaminophen) and its Effect on the Developing Mouse Brain

Paracetamol, or acetaminophen (AAP), is the most commonly used analgesic during pregnancy and early life. While therapeutic doses of AAP are considered harmless during these periods, recent findings in both humans and rodents suggest a link between developmental exposure to AAP and behavioral consequences later in life. The aim of this study is to evaluate the impact of neonatal exposure to clinically relevant doses of AAP on adult spontaneous behavior, habituation, memory, learning, and cognitive flexibility later in life using a mouse model. Markers of oxidative stress, axon outgrowth, and glutamatergic transmission were also investigated in the hippocampus during the first 24 h after exposure. In addition, potential long-term effects on synaptic density in the hippocampus have been investigated. In a home cage setting, mice neonatally exposed to AAP (30 + 30 mg/kg, 4 h apart) on postnatal day 10 displayed altered spontaneous behavior and changed habituation patterns later in life compared to controls. These mice also displayed reduced memory, learning and cognitive flexibility compared to control animals in the Morris water maze. An increase of markers for oxidative stress was observed in the hippocampus 6 h after AAP exposure. As AAP is the first choice treatment for pain and/or fever during pregnancy and early life, these results may be of great importance for risk assessment. Here we show that AAP can have persistent negative effects on brain development and suggest that AAP, despite the relatively low doses, is capable to induce acute oxidative stress in the hippocampus.

Synapse Maturation and Developmental Impairment in the Medial Nucleus of the Trapezoid Body

Sound localization requires rapid interpretation of signal speed, intensity, and frequency. Precise neurotransmission of auditory signals relies on specialized auditory brainstem synapses including the calyx of Held, the large encapsulating input to principal neurons in the medial nucleus of the trapezoid body (MNTB). During development, synapses in the MNTB are established, eliminated, and strengthened, thereby forming an excitatory/inhibitory (E/I) synapse profile. However, in neurodevelopmental disorders such as autism spectrum disorder (ASD), E/I neurotransmission is altered, and auditory phenotypes emerge anatomically, molecularly, and functionally. Here we review factors required for normal synapse development in this auditory brainstem pathway and discuss how it is affected by mutations in ASD-linked genes.

Pleiotropic effects of BDNF on the cerebellum and hippocampus: Implications for neurodevelopmental disorders

Brain-derived neurotrophic factor (BDNF) is one of the most studied neurotrophins in the mammalian brain, essential not only to the development of the central nervous system but also to synaptic plasticity. BDNF is present in various brain areas, but highest levels of expression are seen in the cerebellum and hippocampus. After birth, BDNF acts in the cerebellum as a mitogenic and chemotactic factor, stimulating the cerebellar granule cell precursors to proliferate, migrate and maturate, while in the hippocampus BDNF plays a fundamental role in synaptic transmission and plasticity, representing a key regulator for the long-term potentiation, learning and memory. Furthermore, the expression of BDNF is highly regulated and changes of its expression are associated with both physiological and pathological conditions. The purpose of this review is to provide an overview of the current state of knowledge on the BDNF biology and its neurotrophic role in the proper development and functioning of neurons and synapses in two important brain areas of postnatal neurogenesis, the cerebellum and hippocampus. Dysregulation of BDNF expression and signaling, resulting in alterations in neuronal maturation and plasticity in both systems, is a common hallmark of several neurodevelopmental diseases, such as autism spectrum disorder, suggesting that neuronal malfunction present in these disorders is the result of excessive or reduced of BDNF support. We believe that the more the relevance of the pathophysiological actions of BDNF, and its downstream signals, in early postnatal development will be highlighted, the more likely it is that new neuroprotective therapeutic strategies will be identified in the treatment of various neurodevelopmental disorders.

Effect of 2,6-xylidine (DMA) on secretion of biomarkers for inflammation and neurodevelopment by the placenta

Cigarette smoke enhances placental inflammation and interferes with steroidogenesis. However, the chemicals in the smoke responsible for these biological activities are unclear. 2,6 xylidine (also called 2,6 Dimethylaniline, DMA) is a component of cigarette smoke that has carcinogenic properties but its effects on the placenta are unknown. Therefore, we hypothesized that DMA may interfere with placental steroidogenesis or enhance placental inflammation. Placental explant cultures were treated with 0-50,000 nM DMA and concentrations of progesterone (P₄), estradiol (E₂), testosterone (T), IL-1β, TNF-α, IL-6, sgp130, HO-1, IL-10, 8-Isoprostane (8-IsoP), and BDNF in the conditioned medium were quantified. Since many environmental toxins enhance the proinflammatory host response to infection, we also performed experiments on placental cultures co-stimulated with 10⁷ heat-killed E. coli. DMA alone significantly reduced P₄ and T secretion but enhanced E₂ secretion. The toxin also reduced placental secretion of IL-6, sgp130, and BDNF. For bacteria-stimulated cultures, DMA increased secretion of P₄ and T, and proinflammatory cytokines (IL-1β, TNF-α) but had mixed effects on anti-inflammatory markers, increasing some (sgp130, IL-10) and reducing others (HO-1). However, DMA enhanced 8-IsoP levels by bacteria-stimulated placental cultures, suggesting that it increases oxidative stress by the tissues. These studies suggest that DMA affects secretion of biomarkers by the placenta and may promote inflammation. Further studies are needed to determine if these observed changes occur in vivo and the extent to which DMA exposure increases the risk of adverse pregnancy outcomes associated with smoking in pregnancy.

Symptomatic, Genetic, and Mechanistic Overlaps between Autism and Alzheimer's Disease

Autism spectrum disorder (ASD) and Alzheimer's disease (AD) are neurodevelopmental and neurodegenerative disorders affecting two opposite ends of life span, i.e., childhood and old age. Both disorders pose a cumulative threat to human health, with the rate of incidences increasing considerably worldwide. In the context of recent developments, we aimed to review correlated symptoms and genetics, and overlapping aspects in the mechanisms of the pathogenesis of ASD and AD. Dementia, insomnia, and weak neuromuscular interaction, as well as communicative and cognitive impairments, are shared symptoms. A number of genes and proteins linked with both disorders have been tabulated, including MECP2, ADNP, SCN2A, NLGN, SHANK, PTEN, RELN, and FMR1. Theories about the role of neuron development, processing, connectivity, and levels of neurotransmitters in both disorders have been discussed. Based on the recent literature, the roles of FMRP (Fragile X mental retardation protein), hnRNPC (heterogeneous ribonucleoprotein-C), IRP (Iron regulatory proteins), miRNAs (MicroRNAs), and α-, β0, and γ-secretases in the posttranscriptional regulation of cellular synthesis and processing of APP (amyloid-β precursor protein) have been elaborated to describe the parallel and overlapping routes and mechanisms of ASD and AD pathogenesis. However, the interactive role of genetic and environmental factors, oxidative and metal ion stress, mutations in the associated genes, and alterations in the related cellular pathways in the development of ASD and AD needs further investigation.

Combining in vitro assays and mathematical modelling to study developmental neurotoxicity induced by chemical mixtures

Prenatal and postnatal co-exposure to multiple chemicals at the same time may have deleterious effects on the developing nervous system. We previously showed that chemicals acting through similar mode of action (MoA) and grouped based on perturbation of brain derived neurotrophic factor (BDNF), induced greater neurotoxic effects on human induced pluripotent stem cell (hiPSC)-derived neurons and astrocytes compared to chemicals with dissimilar MoA. Here we assessed the effects of repeated dose (14 days) treatments with mixtures containing the six chemicals tested in our previous study (Bisphenol A, Chlorpyrifos, Lead(II) chloride, Methylmercury chloride, PCB138 and Valproic acid) along with 2,2'4,4'-tetrabromodiphenyl ether (BDE47), Ethanol, Vinclozolin and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)), on hiPSC-derived neural stem cells undergoing differentiation toward mixed neurons/astrocytes up to 21 days. Similar MoA chemicals in mixtures caused an increase of BDNF levels and neurite outgrowth, and a decrease of synapse formation, which led to inhibition of electrical activity. Perturbations of these endpoints are described as common key events in adverse outcome pathways (AOPs) specific for DNT. When compared with mixtures tested in our previous study, adding similarly acting chemicals (BDE47 and EtOH) to the mixture resulted in a stronger downregulation of synapses. A synergistic effect on some synaptogenesis-related features (PSD95 in particular) was hypothesized upon treatment with tested mixtures, as indicated by mathematical modelling. Our findings confirm that the use of human iPSC-derived mixed neuronal/glial models applied to a battery of in vitro assays anchored to key events in DNT AOP networks, combined with mathematical modelling, is a suitable testing strategy to assess in vitro DNT induced by chemical mixtures.

Elevated levels of cortisol, brain-derived neurotropic factor and tissue plasminogen activator in male children with autism spectrum disorder

Several studies demonstrated biological effects of cortisol, brain-derived neurotrophic factor (BDNF) and tissue plasminogen activator (tPA) on human metabolism and central nervous system. Our study investigated the serum levels of tPA along with BDNF and cortisol in children with autism spectrum disorder (ASD). Thirty three male children with ASD ranging in age from 2 to 15 years were selected for the study group and 27 age-matched healthy male children were selected for the control group. The ASD severity was determined by the score on the Autism Behavior Checklist (ABC). The mean cortisol levels for the study group and the control group were 79.1 ± 30.2 ng/ml and 60.0 ± 25.1 ng/ml, respectively. The mean BDNF levels for the study group and the control group were 5.9 ± 2.8 ng/ml and 3.7 ± 1.8 ng/ml, respectively. The mean tPA levels for the study group and the control group were 32.9 ± 18.5 ng/ml and 25.5 ± 15.1 ng/ml, respectively. Cortisol, BDNF and tPA levels were significantly higher in the study group compared to the control group (p < 0.001). There was no statistically significant effect in terms of age, ABC total and subscale scores on serum cortisol, BDNF and tPA levels in the study group (p > 0.05). It may be suggested that elevations may indicate a role in the pathogenesis of ASD or it may be the case that ASD may alter the levels or pathways of these metabolic factors. LAY SUMMARY: The underlying mechanism or a specific metabolic target relevant to autism spectrum disorder (ASD) has not yet been identified. Cortisol, brain-derived neurotrophic factor (BDNF) and tissue plasminogen activator (tPA) have biological effects on neuroplasticity but little is known about the role of cortisol and tPA-BDNF pathway in ASD. In the present study focused on male children with ASD, we have found higher blood levels of cortisol, BDNF and tPA than their healthy peers. This is the first clinical study to evaluate the serum tPA levels along with BDNF and cortisol in ASD. The results suggest that several neurotrophic and other related markers should be born in mind while examining children with ASD.

Plasma levels of nerve growth factor in Egyptian autistic children: Relation to hyperserotonemia and autoimmunity

Hyperserotonemia and brain-specific autoantibodies are detected in some autistic children. Nerve growth factor (NGF) stimulates the proliferation of B lymphocytes with production of antibodies and also increases mast cell serotonin release. This work was the first to investigate the relationship between plasma NGF and both hyperserotonemia and the frequency of serum anti-myelin basic protein (anti-MBP) auto-antibodies in 22 autistic children aged between 4 and 12 years and 22 healthy-matched controls. Levels of NGF, serotonin and anti-MBP were significantly higher in autistic children than healthy control children (P < 0.001). There was a significant positive correlation between NGF and serotonin levels in autistic patients (P < 0.01). In contrast, there was a non-significant correlation between NGF and anti-MBP levels (P > 0.05). In conclusions, serum NGF levels were elevated and significantly correlated to hyperserotonemia found in many autistic children.

Association of neonatal blood levels of brain-derived neurotrophic factor with development of autism spectrum disorder: a systematic review and meta-analysis

BACKGROUND

Our goal was to evaluate the association between neonatal blood brain-derived neurotrophic factor (BDNF) level and autism spectrum disorder (ASD) diagnosis later in life.

METHODS

MEDLINE and Web of Science databases were searched from inception until September 16, 2020. Reference lists of all relevant articles also were reviewed. Mean blood BDNF concentrations, standard deviations, sample sizes, and other data needed for calculation of effect sizes were extracted by two independent investigators. The quality of the included studies was appraised using the Newcastle-Ottawa Scale for case-control studies. Data were pooled using the random-effects model.

RESULTS

Five case-control studies involving 1341 cases and 3395 controls were included in the meta-analysis. The meta-analysis of all included studies showed no significant difference in blood BDNF levels between neonates diagnosed with ASD later in life and healthy controls [standardized mean difference (SMD) = 0.261; 95% confidence interval (CI) - 0.052 to 0.573; P = 0.102], with high level of heterogeneity (Q = 64.346; I² = 93.784; P < 0.001). A subgroup analysis by assay type showed decreased blood BDNF levels in ASDs compared to controls (SMD = - 0.070; 95% CI - 0.114 to - 0.026; P = 0.002), with high level of homogeneity (Q = 0.894; I² = 0.000; P = 0.827). No evidence of publication bias was observed.

CONCLUSIONS

Neonates diagnosed with ASD later in life have decreased blood levels of BDNF measured by double-antibody immunoassay. More studies are warranted to facilitate a more robust conclusion.

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.

Nutritional Neuroscience as Mainstream of Psychiatry: The Evidence- Based Treatment Guidelines for Using Omega-3 Fatty Acids as a New Treatment for Psychiatric Disorders in Children and Adolescents

Omega-3 polyunsaturated fatty acids (or omega-3 PUFAs, n-3 PUFAs) are essential nutrients throughout the life span. Recent studies have shown the importance of n-3 PUFAs supplementation during prenatal and perinatal period as a potential protective factor of neurodevelopmental disorders. N-3 PUFAs have been reported to be lower in youth with attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD) and major depressive disorder (MDD). N-3 PUFAs supplementation has shown potential effects in the improvement of clinical symptoms in youth with ADHD, ASD, and MDD, especially those with high inflammation or a low baseline n-3 index. Moreover, it has been suggested that n-3 PUFAs had positive effects on lethargy and hyperactivity symptoms in ASD. For clinical application, the following dosage and duration are recommended in youth according to available randomized controlled trials and systemic literature review: (1) ADHD: a combination of eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) ≥ 750 mg/d, and a higher dose of EPA (1,200 mg/d) for those with inflammation or allergic diseases for duration of 16−24 weeks; (2) MDD: a combination of a EPA + DHA of 1,000−2,000 mg/d, with EPA:DHA ratio of 2 to 1, for 12−16 weeks; (3) ASD: a combination of EPA + DHA of 1,300−1,500 mg/d for 16−24 weeks as add-on therapy to target lethargy and hyperactivity symptoms. The current review also suggested that n-3 index and inflammation may be potential treatment response markers for youth, especially in ADHD and MDD, receiving n-3 PUFA.

Assessment of BDNF serum levels as a diagnostic marker in children with autism spectrum disorder

There has been a significant increase in autism spectrum disorder (ASD) in the last decades that cannot be exclusively attributed to better diagnosis and an increase in the communication of new cases. Patients with ASD often show dysregulation of proteins associated with synaptic plasticity, notably brain-derived neurotrophic factor (BDNF). The objective of the present study was to analyze BDNF serum concentration levels in children with classic forms autism and a healthy control group to determine if there is a correlation between ASD and BDNF serum levels. Forty-nine children with severe classic form of autism, and 37 healthy children were enrolled in the study. Blood samples, from both patients and controls, were collected and BNDF levels from both groups were analyzed. The average BDNF serum concentration level was statistically higher for children with ASD (P < 0.000) compared to the control group. There is little doubt that BDNF plays a role in the pathophysiology of ASD development and evolution, but its brain levels may fluctuate depending on several known and unknown factors. The critical question is not if BDNF levels can be considered a prognostic or diagnostic marker of ASD, but to determine its role in the onset and progression of this disorder.

Endocrinological Abnormalities in Autism

A number of chemical messengers, such as various hormones and hormone-like substances, along with neurotransmitters, such as serotonin, dopamine, and norepinephrine, are directly or indirectly linked with the encoding of social behavior via their action at the amygdala, hippocampus, and other related brain structures known to be involved in different aspects of social development. It is thought that any imbalance in the secretion and action of these chemicals may lead to defective or abnormal social behaviors that are the hallmarks of Autism Spectrum Disorders (ASDs). Many of the studies have described an association between ASDs and endocrine dysfunction, but have failed to establish a cause-effect connection between these 2 conditions. All together, the literature regarding the role of endocrine-related factors and ASDs is sparse and remains somewhat preliminary, controversial, and inconclusive. Thus, more research is needed in the future to shed more light on this topic.

Assessment of developmental neurotoxicity induced by chemical mixtures using an adverse outcome pathway concept

BACKGROUND

In light of the vulnerability of the developing brain, mixture risk assessment (MRA) for the evaluation of developmental neurotoxicity (DNT) should be implemented, since infants and children are co-exposed to more than one chemical at a time. One possible approach to tackle MRA could be to cluster DNT chemicals in a mixture on the basis of their mode of action (MoA) into 'similar' and 'dissimilar', but still contributing to the same adverse outcome, and anchor DNT assays to common key events (CKEs) identified in DNT-specific adverse outcome pathways (AOPs). Moreover, the use of human in vitro models, such as induced pluripotent stem cell (hiPSC)-derived neuronal and glial cultures would enable mechanistic understanding of chemically-induced adverse effects, avoiding species extrapolation.

METHODS

HiPSC-derived neural progenitors differentiated into mixed cultures of neurons and astrocytes were used to assess the effects of acute (3 days) and repeated dose (14 days) treatments with single chemicals and in mixtures belonging to different classes (i.e., lead(II) chloride and methylmercury chloride (heavy metals), chlorpyrifos (pesticide), bisphenol A (organic compound and endocrine disrupter), valproic acid (drug), and PCB138 (persistent organic pollutant and endocrine disrupter), which are associated with cognitive deficits, including learning and memory impairment in children. Selected chemicals were grouped based on their mode of action (MoA) into 'similar' and 'dissimilar' MoA compounds and their effects on synaptogenesis, neurite outgrowth, and brain derived neurotrophic factor (BDNF) protein levels, identified as CKEs in currently available AOPs relevant to DNT, were evaluated by immunocytochemistry and high content imaging analysis.

RESULTS

Chemicals working through similar MoA (i.e., alterations of BDNF levels), at non-cytotoxic (IC20/100), very low toxic (IC5), or moderately toxic (IC20) concentrations, induce DNT effects in mixtures, as shown by increased number of neurons, impairment of neurite outgrowth and synaptogenesis (the most sensitive endpoint as confirmed by mathematical modelling) and increase of BDNF levels, to a certain extent reproducing autism-like cellular changes observed in the brain of autistic children.

CONCLUSIONS

Our findings suggest that the use of human iPSC-derived mixed neuronal/glial cultures applied to a battery of assays anchored to key events of an AOP network represents a valuable approach to identify mixtures of chemicals with potential to cause learning and memory impairment in children.

Expression Analysis of BDNF, BACE1, and Their Natural Occurring Antisenses in Autistic Patients

Autism spectrum disorder (ASD) as a multifaceted neurological syndrome affects many aspects of neuropsychologic functions. Dysregulated expressions of several genes have been documented in ASD patients. The current project aimed at comparison of transcript levels of brain derived neurotrophic factor (BDNF), beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), and their natural occurring antisenses in the peripheral blood of ASD individuals (n = 50, male/female = 38/12, age (mean ± standard deviation (SD)): 6 ± 1.4, age range: 3-8) and matched healthy persons (n = 50, male/female = 37/13, age (mean ± SD): 6 ± 1.74, age range: 3-8). We demonstrated remarkable higher levels of these genes in ASD patients. BACE1 transcript levels were correlated with transcript levels of BACE1-AS in all study participants. However, BACE1 transcript levels were not correlated with participants' age. BACE1-AS and BDNF transcript levels were correlated with age in female participants. Significant correlations were detected between transcript levels of BDNF and those of other genes in all study groups. The current results render further indications for contribution of BDNF, BACE1, and their antisenses in the course of ASD and suggested expression levels of these transcripts as putative markers for this neurobehavioral disorder. Such results might be applied in clinical setting for diagnosis of complicated ASD cases.

Are preconceptional stressful experiences crucial elements for the aetiology of autism spectrum disorder? Insights from an animal model

Autism spectrum disorders (ASD) are a group of neurodevelopmental disorders characterized by changes in social interactions, impaired language and communication, fear responses and presence of repetitive behaviours. Although the genetic bases of ASD are well documented, the recent increase in clinical cases of idiopathic ASD indicates that several environmental risk factors could play a role in ASD aetiology. Among these, maternal exposure to psychosocial stressors during pregnancy has been hypothesized to affect the risk for ASD in offspring. Here, we tested the hypothesis that preconceptional stressful experiences might also represent crucial elements in the aetiology of ASD. We previously showed that social isolation stress during adolescence results in a marked decrease in the brain and plasma concentrations of progesterone and in the quality of maternal care that these female rats later provide to their young. Here we report that male offspring of socially isolated parents showed decreased agonistic behaviour and social transmission of flavour preference, impairment in reversal learning, increased seizure susceptibility, reduced plasma oxytocin levels, and increased plasma and brain levels of BDNF, all features resembling an ASD-like phenotype. These alterations came with no change in spatial learning, aggression, anxiety and testosterone plasma levels, and were sex-dependent. Altogether, the results suggest that preconceptional stressful experiences should be considered as crucial elements for the aetiology of ASD, and indicate that male offspring of socially isolated parents may be a useful animal model to further study the neurobiological bases of ASD, avoiding the adaptations that may occur in other genetic or pharmacologic experimental models of these disorders.

Nutritional modulation of the intestinal microbiota; future opportunities for the prevention and treatment of neuroimmune and neuroinflammatory disease

The gut-brain axis refers to the bidirectional communication between the enteric nervous system and the central nervous system. Mounting evidence supports the premise that the intestinal microbiota plays a pivotal role in its function and has led to the more common and perhaps more accurate term gut-microbiota-brain axis. Numerous studies have identified associations between an altered microbiome and neuroimmune and neuroinflammatory diseases. In most cases, it is unknown if these associations are cause or effect; notwithstanding, maintaining or restoring homeostasis of the microbiota may represent future opportunities when treating or preventing these diseases. In recent years, several studies have identified the diet as a primary contributing factor in shaping the composition of the gut microbiota and, in turn, the mucosal and systemic immune systems. In this review, we will discuss the potential opportunities and challenges with respect to modifying and shaping the microbiota through diet and nutrition in order to treat or prevent neuroimmune and neuroinflammatory disease.

Brain-derived neurotrophic factor (BDNF) in children with ASD and their parents: a 3-year follow-up

OBJECTIVE

Several lines of evidence point to a probable relationship between brain-derived neurotrophic factor (BDNF) and autism spectrum disorder (ASD), but studies have yielded inconsistent findings on the BDNF serum level in ASD. The study aimed to assess those levels in children with ASD and their families.

METHOD

BDNF serum levels were measured in 45 ASD children without intellectual disability (ID) and allergies, age 30-42 months and age-matched normal controls. BDNF serum levels in the parents of the ASD subjects were compared to normal controls. BDNF serum levels in the ASD subjects were followed up for 3 years and correlated with adaptive functioning changes.

RESULTS

BDNF serum levels were measured to be lower in children with ASD and independent of all the major baseline characteristics of the subjects. Having a child with ASD raises the BDNF levels in parents comparing to controls. Prospectively, no correlation between the change of BDNF variables in time and the change of the Vineland scores was found.

CONCLUSIONS

Our results contradict those from recent published meta-analyses with the age, the presence of ID and allergies being possible contributing factors. The parents' data indeed point to a role of BDNF in the pathophysiology of ASD.

Prenatal paracetamol exposure and child neurodevelopment: A review

BACKGROUND

The non-prescription medication paracetamol (acetaminophen, APAP) is currently recommended as a safe pain and fever treatment during pregnancy. However, recent studies suggest a possible association between APAP use in pregnancy and offspring neurodevelopment.

OBJECTIVES

To conduct a review of publications reporting associations between prenatal APAP use and offspring neurodevelopmental outcomes.

METHODS

Relevant sources were identified through a key word search of multiple databases (Medline, CINAHL, OVID and TOXNET) in September 2016. All English language observational studies of pregnancy APAP and three classes of neurodevelopmental outcomes (autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), and intelligence quotient (IQ)) were included. One reviewer (AZB) independently screened all titles and abstracts, extracted and analyzed the data.

RESULTS

64 studies were retrieved and 55 were ineligible. Nine prospective cohort studies fulfilled all inclusion criteria. Data pooling was not appropriate due to heterogeneity in outcomes. All included studies suggested an association between prenatal APAP exposure and the neurodevelopmental outcomes; ADHD, ASD, or lower IQ. Longer duration of APAP use was associated with increased risk. Associations were strongest for hyperactivity and attention-related outcomes. Little modification of associations by indication for use was reported.

CONCLUSIONS

Together, these nine studies suggest an increased risk of adverse neurodevelopmental outcomes following prenatal APAP exposure. Further studies are urgently needed with; precise indication of use and exposure assessment of use both in utero and in early life. Given the current findings, pregnant women should be cautioned against indiscriminate use of APAP. These results have substantial public health implications.

Developmental origins of adult health and disease: The metabolic role of BDNF from early life to adulthood

Accumulating evidence suggests that the origins of adult disease may occur during fetal life. Thus, the concept of "developmental programming" has been introduced and supported by epidemiological and experimental data. This concept supports the idea that the nutritional and hormonal status during pregnancy could interfere in metabolism control. The mechanisms responsible for this "developmental programming" remain poorly documented. Current research indicates that neurotrophins and particularly brain-derived neurotrophic factor (BDNF) may play a crucial role in this process. Although mainly expressed in the nervous system, BDNF and its receptor, tropomyosin-related kinase B (TrkB), are immunolocalized in several regions of the human placenta and have important functions during pregnancy. BDNF serves widespread roles in regulating energy homeostasis in both fetuses and adults, by controlling patterns of fetal growth, adult feeding and physical activity, and by regulating glucose metabolism in peripheral tissues. Impaired BDNF signaling may be implicated in the etiopathogenesis of the metabolic syndrome. Novel BDNF-focused interventions are being developed for obesity, diabetes and neurological disorders. The aim of this article is to provide a brief comprehensive literary review regarding the potential implications of BDNF in "developmental programming", through regulation of metabolism and energy balance from early life to adulthood.

Differential Behavioral and Biochemical Responses to Caffeine in Male and Female Rats from a Validated Model of Attention Deficit and Hyperactivity Disorder

Epidemiological studies suggest sex differences in attention deficit and hyperactivity disorder (ADHD) symptomatology. The potential benefits of caffeine have been reported in the management of ADHD, but its effects were not properly addressed with respect to sex differences. The present study examined the effects of caffeine (0.3 g/L) administered since childhood in the behavior and brain-derived neurotrophic factor (BDNF) and its related proteins in both sexes of a rat model of ADHD (spontaneously hypertensive rats-SHR). Hyperlocomotion, recognition, and spatial memory disturbances were observed in adolescent SHR rats from both sexes. However, females showed lack of habituation and worsened spatial memory. Although caffeine was effective against recognition memory impairment in both sexes, spatial memory was recovered only in female SHR rats. Besides, female SHR rats showed exacerbated hyperlocomotion after caffeine treatment. SHR rats from both sexes presented increases in the BDNF, truncated and phospho-TrkB receptors and also phospho-CREB levels in the hippocampus. Caffeine normalized BDNF in males and truncated TrkB receptor at both sexes. These findings provide insight into the potential of caffeine against fully cognitive impairment displayed by females in the ADHD model. Besides, our data revealed that caffeine intake since childhood attenuated behavioral alterations in the ADHD model associated with changes in BDNF and TrkB receptors in the hippocampus.

Meta-Analysis of BDNF Levels in Autism

Brain-derived neurotrophic factor (BDNF) centrally mediates growth, differentiation and survival of neurons, and the synaptic plasticity that underlies learning and memory. Recent meta-analyses have reported significantly lower peripheral BDNF among individuals with schizophrenia, bipolar disorder, and depression, compared with controls. To evaluate the role of BDNF in autism, and to compare autism to psychotic-affective disorders with regard to BDNF, we conducted a meta-analysis of BDNF levels in autism. Inclusion criteria were met by 15 studies, which included 1242 participants. The meta-analysis estimated a significant summary effect size of 0.33 (95 % CI 0.21-0.45, P < 0.001), suggesting higher BDNF in autism than in controls. The studies showed notable heterogeneity, but no evidence of publication biases. Higher peripheral BDNF in autism is concordant with several neurological and psychological theories on the causes and symptoms of this condition, and it contrasts notably with the lower levels of BDNF found in schizophrenia, bipolar disorder, and depression.

Relationship between Long Chain n-3 Polyunsaturated Fatty Acids and Autism Spectrum Disorder: Systematic Review and Meta-Analysis of Case-Control and Randomised Controlled Trials

Omega-3 long chain polyunsaturated fatty acid supplementation (n-3 LCPUFA) for treatment of Autism Spectrum Disorder (ASD) is popular. The results of previous systematic reviews and meta-analyses of n-3 LCPUFA supplementation on ASD outcomes were inconclusive. Two meta-analyses were conducted; meta-analysis 1 compared blood levels of LCPUFA and their ratios arachidonic acid (ARA) to docosahexaenoic acid (DHA), ARA to eicosapentaenoic acid (EPA), or total n-6 to total n-3 LCPUFA in ASD to those of typically developing individuals (with no neurodevelopmental disorders), and meta-analysis 2 compared the effects of n-3 LCPUFA supplementation to placebo on symptoms of ASD. Case-control studies and randomised controlled trials (RCTs) were identified searching electronic databases up to May, 2016. Mean differences were pooled and analysed using inverse variance models. Heterogeneity was assessed using I² statistic. Fifteen case-control studies (n = 1193) were reviewed. Compared with typically developed, ASD populations had lower DHA (−2.14 [95% CI −3.22 to −1.07]; p < 0.0001; I² = 97%), EPA (−0.72 [95% CI −1.25 to −0.18]; p = 0.008; I² = 88%), and ARA (−0.83 [95% CI, −1.48 to −0.17]; p = 0.01; I² = 96%) and higher total n-6 LCPUFA to n-3 LCPUFA ratio (0.42 [95% CI 0.06 to 0.78]; p = 0.02; I² = 74%). Four RCTs were included in meta-analysis 2 (n = 107). Compared with placebo, n-3 LCPUFA improved social interaction (−1.96 [95% CI −3.5 to −0.34]; p = 0.02; I² = 0) and repetitive and restricted interests and behaviours (−1.08 [95% CI −2.17 to −0.01]; p = 0.05; I² = 0). Populations with ASD have lower n-3 LCPUFA status and n-3 LCPUFA supplementation can potentially improve some ASD symptoms. Further research with large sample size and adequate study duration is warranted to confirm the efficacy of n-3 LCPUFA.

Severity of ASD symptoms and their correlation with the presence of copy number variations and exposure to first trimester ultrasound

Current research suggests that incidence and heterogeneity of autism spectrum disorder (ASD) symptoms may arise through a variety of exogenous and/or endogenous factors. While subject to routine clinical practice and generally considered safe, there exists speculation, though no human data, that diagnostic ultrasound may also contribute to ASD severity, supported by experimental evidence that exposure to ultrasound early in gestation could perturb brain development and alter behavior. Here we explored a modified triple hit hypothesis [Williams & Casanova, ] to assay for a possible relationship between the severity of ASD symptoms and (1) ultrasound exposure (2) during the first trimester of pregnancy in fetuses with a (3) genetic predisposition to ASD. We did so using retrospective analysis of data from the SSC (Simon's Simplex Collection) autism genetic repository funded by the Simons Foundation Autism Research Initiative. We found that male children with ASD, copy number variations (CNVs), and exposure to first trimester ultrasound had significantly decreased non-verbal IQ and increased repetitive behaviors relative to male children with ASD, with CNVs, and no ultrasound. These data suggest that heterogeneity in ASD symptoms may result, at least in part, from exposure to diagnostic ultrasound during early prenatal development of children with specific genetic vulnerabilities. These results also add weight to on-going concerns expressed by the FDA about non-medical use of diagnostic ultrasound during pregnancy. Autism Res 2017, 10: 472-484. © 2016 International Society for Autism Research, Wiley Periodicals, Inc.

Brain-derived neurotrophic factor signaling is altered in the forebrain of Engrailed-2 knockout mice

Engrailed-2 (En2), a homeodomain transcription factor involved in regionalization and patterning of the midbrain and hindbrain regions has been associated to autism spectrum disorders (ASDs). En2 knockout (En2(-/-)) mice show ASD-like features accompanied by a significant loss of GABAergic subpopulations in the hippocampus and neocortex. Brain-derived neurotrophic factor (BDNF) is a crucial factor for the postnatal development of forebrain GABAergic neurons, and altered GABA signaling has been hypothesized to underlie the symptoms of ASD. Here we sought to determine whether interneuron loss in the En2(-/-) forebrain might be related to altered expression of BDNF and its signaling receptors. We first evaluated the expression of different BDNF mRNA isoforms in the neocortex and hippocampus of wild-type (WT) and En2(-/-) mice. Quantitative RT-PCR showed a marked down-regulation of several splicing variants of BDNF mRNA in the neocortex but not hippocampus of adult En2(-/-) mice, as compared to WT controls. Accordingly, levels of mature BDNF protein were lower in the neocortex but not hippocampus of En2(-/-) mice, as compared to WT. Increased levels of phosphorylated TrkB and decreased levels of p75 receptor were also detected in the neocortex of mutant mice. Accordingly, the expression of low density lipoprotein receptor (LDLR) and RhoA, two genes regulated via p75 was significantly altered in forebrain areas of mutant mice. These data indicate that BDNF signaling alterations might be involved in the anatomical changes observed in the En2(-/-) forebrain and suggest a pathogenic role of altered BDNF signaling in this mouse model of ASD.

Clinical and Neurobiological Relevance of Current Animal Models of Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by social and communication impairments, as well as repetitive and restrictive behaviors. The phenotypic heterogeneity of ASD has made it overwhelmingly difficult to determine the exact etiology and pathophysiology underlying the core symptoms, which are often accompanied by comorbidities such as hyperactivity, seizures, and sensorimotor abnormalities. To our benefit, the advent of animal models has allowed us to assess and test diverse risk factors of ASD, both genetic and environmental, and measure their contribution to the manifestation of autistic symptoms. At a broader scale, rodent models have helped consolidate molecular pathways and unify the neurophysiological mechanisms underlying each one of the various etiologies. This approach will potentially enable the stratification of ASD into clinical, molecular, and neurophenotypic subgroups, further proving their translational utility. It is henceforth paramount to establish a common ground of mechanistic theories from complementing results in preclinical research. In this review, we cluster the ASD animal models into lesion and genetic models and further classify them based on the corresponding environmental, epigenetic and genetic factors. Finally, we summarize the symptoms and neuropathological highlights for each model and make critical comparisons that elucidate their clinical and neurobiological relevance.

DNA methylation: a mechanism linking environmental chemical exposures to risk of autism spectrum disorders?

There is now compelling evidence that gene by environment interactions are important in the etiology of autism spectrum disorders (ASDs). However, the mechanisms by which environmental factors interact with genetic susceptibilities to confer individual risk for ASD remain a significant knowledge gap in the field. The epigenome, and in particular DNA methylation, is a critical gene expression regulatory mechanism in normal and pathogenic brain development. DNA methylation can be influenced by environmental factors such as diet, hormones, stress, drugs, or exposure to environmental chemicals, suggesting that environmental factors may contribute to adverse neurodevelopmental outcomes of relevance to ASD via effects on DNA methylation in the developing brain. In this review, we describe epidemiological and experimental evidence implicating altered DNA methylation as a potential mechanism by which environmental chemicals confer risk for ASD, using polychlorinated biphenyls (PCBs), lead, and bisphenol A (BPA) as examples. Understanding how environmental chemical exposures influence DNA methylation and how these epigenetic changes modulate the risk and/or severity of ASD will not only provide mechanistic insight regarding gene-environment interactions of relevance to ASD but may also suggest potential intervention strategies for these and potentially other neurodevelopmental disorders.

Elevated Serum Brain-Derived Neurotrophic Factor (BDNF) but not BDNF Gene Val66Met Polymorphism Is Associated with Autism Spectrum Disorders

The aim of our study was to illuminate the potential role of brain-derived neurotrophic factor (BDNF) in autism spectrum disorder (ASD). We measured the circulating levels of BDNF in serum and BDNF gene (Val66Met) polymorphisms, in which two indicators were then compared between ASD and normal controls. A total of 82 drug-naïve ASD children and 82 age- and gender-matched normal controls were enrolled in the study. Their serum BDNF levels were detected by the ELISA. BDNF Val66Met polymorphism genotyping was conducted as according to the laboratory's standard protocol in laboratory. The ASD severity assessment was mainly determined by the score of the Childhood Autism Rating Scale (CARS). ELISA assay showed that the mean serum BDNF level of children with ASD was significantly (P < 0.0001) higher than that of the control cases (17.75 ± 5.43 vs. 11.49 ± 2.85 ng/ml; t = 9.236). Besides, the serum BDNF levels and CARS scores (P < 0.0001) were positively related. And, the BDNF genotyping results showed that there was no difference between the ASD cases and the control. Among the children with ASD, the mean serum BDNF level of Met/Met group was lower than other groups. According to the ROC curve generated from our clinical data, the optimal cutoff value of serum BDNF levels, an indicator for diagnosis of ASD, was projected to be 12.50 ng/ml. Thus, it yielded a corresponding sensitivity of 81.7 % and the specificity of 66.9 %. Accordingly, area value under the curve was 0.836 (95 % CI, 0.774-0.897); the positive predictive value (PPV) and the negative predictive value (NPV) were 70.1 and 79.1 %, respectively. These results suggested that rather than Val66Met polymorphism, BDNF was more possible to impact the pathogenesis of ASD.

Roles of phosphoinositide-specific phospholipase Cγ1 in brain development

Over the past decade, converging evidence suggests that PLCγ1 signaling has key roles in controlling neural development steps. PLCγ1 functions as a signal transducer that converts an extracellular stimulus into intracellular signals by generating second messengers such as DAG and IP3. DAG functions as an activator of either PKC or transient receptor potential cation channels (TRPCs), while IP3 induces the calcium release from intracellular calcium stores. These second messengers regulate the morphological change of neuron, such as neurite outgrowth, migration, axon pathfinding, and synapse formation. These morphological changes depend on finely tuned calcium signaling following receptor tyrosine kinase-mediated PLCγ1 signaling. Thus, deregulation of PLCγ1 signaling causes various abnormalities of neuronal development and it may be associated with diverse neurological disorders. Herein, we discuss the current understanding of the PLCγ1 signaling pathway in neural development and provide recent advances of how PLCγ1 signaling is involved in the formation of neuronal processes for functionally faithful brain development.