Serum glutamate was elevated in children aged 3-10 years with autism spectrum disorders when they were compared with controls

Glutamatergic synapse in autism: a complex story for a complex disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder whose pathophysiological mechanisms are still unclear. Hypotheses suggest a role for glutamate dysfunctions in ASD development, but clinical studies investigating brain and peripheral glutamate levels showed heterogenous results leading to hypo- and hyper-glutamatergic hypotheses of ASD. Recently, studies proposed the implication of elevated mGluR5 densities in brain areas in the pathophysiology of ASD. Thus, our objective was to characterize glutamate dysfunctions in adult subjects with ASD by quantifying (1) glutamate levels in the cingulate cortex and periphery using proton magnetic resonance spectroscopy and metabolomics, and (2) mGluR5 brain density in this population and in a validated animal model of ASD (prenatal exposure to valproate) at developmental stages corresponding to childhood and adolescence in humans using positron emission tomography. No modifications in cingulate Glu levels were observed between individuals with ASD and controls further supporting the difficulty to evaluate modifications in excitatory transmission using spectroscopy in this population, and the complexity of its glutamate-related changes. Our imaging results showed an overall increased density in mGluR5 in adults with ASD, that was only observed mostly subcortically in adolescent male rats prenatally exposed to valproic acid, and not detected in the stage corresponding to childhood in the same animals. This suggest that clinical changes in mGluR5 density could reflect the adaptation of the glutamatergic dysfunctions occurring earlier rather than being key to the pathophysiology of ASD.

Autism Spectrum Disorder: Focus on Glutamatergic Neurotransmission

Disturbances in the glutamatergic system have been increasingly documented in several neuropsychiatric disorders, including autism spectrum disorder (ASD). Glutamate-centered theories of ASD are based on evidence from patient samples and postmortem studies, as well as from studies documenting abnormalities in glutamatergic gene expression and metabolic pathways, including changes in the gut microbiota glutamate metabolism in patients with ASD. In addition, preclinical studies on animal models have demonstrated glutamatergic neurotransmission deficits and altered expression of glutamate synaptic proteins. At present, there are no approved glutamatergic drugs for ASD, but several ongoing clinical trials are currently focusing on evaluating in autistic patients glutamatergic pharmaceuticals already approved for other conditions. In this review, we provide an overview of the literature concerning the role of glutamatergic neurotransmission in the pathophysiology of ASD and as a potential target for novel treatments.

C1q/TNF-related protein-1: Potential biomarker for early diagnosis of autism spectrum disorder

INTRODUCTION

Autism spectrum disorders (ASDs) are neurodevelopmental diseases characterized by communication inabilities, social interaction impairment, repetitive behavior, as well as learning problems. Although the exact mechanism underlying this disease is still obscure, researchers believe that several factors play a significant role in its development and pathogenesis. Some authors have reported an association between adipokines family and autism. C1q/TNF-related protein-1 (CTRP1) is a member of the adipokines family, and we hypothesized that this adipokine might have an influential role in the pathogenesis of ASDs. Since there is no specific marker for screening the disease, we evaluated CTRP1 as a potential marker for achieving this purpose.

METHODS

Blood samples were collected from 82 (41 ASDs boys, 41 healthy boys as controls) children aged 5-7 years old. CTRP1 gene expression and CTRP1 serum level were measured by quantitative realtime-PCR and enzyme-linked immunosorbent assay methods, respectively.

RESULTS

It was found that CTRP1 is significantly elevated in autistic children in comparison to healthy controls, both at the gene expression level, as well as at the serum level; demonstrating a good diagnostic value with a good range of sensitivity and specificity for detecting ASDs.

CONCLUSION

CTRP1 expression is elevated in ASDs boys aged 5-7 years old, suggesting a role for this adipokine in ASDs pathophysiology. Also, receiver operating characteristic curve analyses revealed that this adipokine could be utilized as a diagnostic biomarker for differentiating ASDs patients from healthy individuals along with other recently proposed biomarkers.

Sex differences in neuronal systems function and behaviour: beyond a single diagnosis in autism spectrum disorders

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder that is associated with functional brain alterations that underlie the expression of behaviour. Males are diagnosed up to four times more than females, and sex differences have been identified in memory, cognitive flexibility, verbal fluency, and social communication. Unfortunately, there exists a lack of information on the sex-dependent mechanisms of ASD, as well as biological markers to distinguish sex-specific symptoms in ASD. This can often result in a standardized diagnosis for individuals across the spectrum, despite significant differences in the various ASD subtypes. Alterations in neuronal connectivity and oscillatory activity, such as is observed in ASD, are highly coupled to behavioural states. Yet, despite the well-identified sexual dimorphisms that exist in ASD, these functional patterns have rarely been analyzed in the context of sex differences or symptomology. This review summarizes alterations in neuronal oscillatory function in ASD, discusses the age, region, symptom and sex-specific differences that are currently observed across the spectrum, and potential targets for regulating neuronal oscillatory activity in ASD. The need to identify sex-specific biomarkers, in order to facilitate specific diagnostic criteria and allow for more targeted therapeutic approaches for ASD will also be discussed.

Region-specific elevations of glutamate + glutamine correlate with the sensory symptoms of autism spectrum disorders

Individuals on the autism spectrum are often reported as being hyper- and/or hyporeactive to sensory input. These sensory symptoms were one of the key observations that led to the development of the altered excitation-inhibition (E-I) model of autism, which posits that an increase ratio of excitatory to inhibitory signaling may explain certain phenotypical expressions of autism spectrum disorders (ASD). While there has been strong support for the altered E-I model of autism, much of the evidence has come from animal models. With regard to in-vivo human studies, evidence for altered E-I balance in ASD come from studies adopting magnetic resonance spectroscopy (MRS). Spectral-edited MRS can be used to provide measures of the levels of GABA + (GABA + macromolecules) and Glx (glutamate + glutamine) in specific brain regions as proxy markers of inhibition and excitation respectively. In the current study, we found region-specific elevations of Glx in the primary sensorimotor cortex (SM1) in ASD. There were no group differences of GABA+ in either the SM1 or thalamus. Higher levels of Glx were associated with more parent reported difficulties of sensory hyper- and hyporeactivity, as well as reduced feed-forward inhibition during tactile perception in children with ASD. Critically, the finding of elevated Glx provides strong empirical support for increased excitation in ASD. Our results also provide a clear link between Glx and the sensory symptoms of ASD at both behavioral and perceptual levels.

Overexpression of mGluR7 in the Prefrontal Cortex Attenuates Autistic Behaviors in Mice

Autism spectrum disorder (ASD) is associated with a range of abnormalities pertaining to socialization, communication, repetitive behaviors, and restricted interests. Owing to its complexity, the etiology of ASD remains incompletely understood. The presynaptic G protein-coupled glutamate receptor metabotropic glutamate receptor 7 (mGluR7) is known to be essential for synaptic transmission and is also tightly linked with ASD incidence. Herein, we report that prefrontal cortex (PFC) mGluR7 protein levels were decreased in C57BL/6J mice exposed to valproic acid (VPA) and BTBR T⁺ Itpr3^tf/J mice. The overexpression of mGluR7 in the PFC of these mice using a lentiviral vector was sufficient to reduce the severity of ASD-like behavioral patterns such that animals exhibited decreases in abnormal social interactions and communication, anxiety-like, and stereotyped/repetitive behaviors. Intriguingly, patch-clamp recordings revealed that the overexpression of mGluR7 suppressed neuronal excitability by inhibiting action potential discharge frequencies, together with enhanced action potential threshold and increased rheobase. These data offer a scientific basis for the additional study of mGluR7 as a promising therapeutic target in ASD and related neurodevelopmental disorders.

Glutamatergic Dysfunction and Synaptic Ultrastructural Alterations in Schizophrenia and Autism Spectrum Disorder: Evidence from Human and Rodent Studies

The correlation between dysfunction in the glutamatergic system and neuropsychiatric disorders, including schizophrenia and autism spectrum disorder, is undisputed. Both disorders are associated with molecular and ultrastructural alterations that affect synaptic plasticity and thus the molecular and physiological basis of learning and memory. Altered synaptic plasticity, accompanied by changes in protein synthesis and trafficking of postsynaptic proteins, as well as structural modifications of excitatory synapses, are critically involved in the postnatal development of the mammalian nervous system. In this review, we summarize glutamatergic alterations and ultrastructural changes in synapses in schizophrenia and autism spectrum disorder of genetic or drug-related origin, and briefly comment on the possible reversibility of these neuropsychiatric disorders in the light of findings in regular synaptic physiology.

Vitamin C Attenuates Oxidative Stress and Behavioral Abnormalities Triggered by Fipronil and Pyriproxyfen Insecticide Chronic Exposure on Zebrafish Juvenile

Chronic exposure to synthetic insecticides in the early life of a child can lead to a series of disorders. Several causes as parental age, maternal smoking, birth complications, and exposure to toxins such as insecticides on childhood can lead to Autism spectrum disorder (ASD) occurrence. The aim of this study was to evaluate the potential protective role of vitamin C (Vit. C) from children's supplements after 14 days chronic exposure to insecticide mixture fipronil (Fip) + pyriproxyfen (Pyr) on juvenile zebrafish for swimming performances, social behavior and oxidative stress associated with ASD model. Juvenile (14-17 mm) wild-type AB zebrafish (Danio rerio) (45 days) were exposed to relevant concentrations: vit. C (25 µg L-1), Fip (600 µg L-1/1.372 μM) + Pyr (600 µg L-1/1.89 μM), and [Fip (600 µg L-1/1.372 μM) + Pyr (600 µg L-1 /1.89 μM)] + vit. C (25 µg L-1). Our results showed that insecticides can disturb the social behavior of zebrafish during 14 days of the administration, decreased the swimming performances, and elevated the oxidative stress biomarkers of SOD (superoxide dismutase), GPx (glutathione peroxidase), and MDA (malondialdehyde). The vitamin C supplement significantly attenuated the neurotoxicity of insecticide mixture and oxidative stress. This study provides possible in vivo evidence to show that vitamin C supplements could attenuate oxidative stress and brain damage of fipronil and pyriproxyfen insecticide chronic exposure on zebrafish juvenile.

Neuron-Glia Interactions in Neurodevelopmental Disorders

Recent studies have revealed synaptic dysfunction to be a hallmark of various psychiatric diseases, and that glial cells participate in synapse formation, development, and plasticity. Glial cells contribute to neuroinflammation and synaptic homeostasis, the latter being essential for maintaining the physiological function of the central nervous system (CNS). In particular, glial cells undergo gliotransmission and regulate neuronal activity in tripartite synapses via ion channels (gap junction hemichannel, volume regulated anion channel, and bestrophin-1), receptors (for neurotransmitters and cytokines), or transporters (GLT-1, GLAST, and GATs) that are expressed on glial cell membranes. In this review, we propose that dysfunction in neuron-glia interactions may contribute to the pathogenesis of neurodevelopmental disorders. Understanding the mechanisms of neuron-glia interaction for synapse formation and maturation will contribute to the development of novel therapeutic targets of neurodevelopmental disorders.

Dysfunctional d-aspartate metabolism in BTBR mouse model of idiopathic autism

BACKGROUND

Autism spectrum disorders (ASD) comprise a heterogeneous group of neurodevelopmental conditions characterized by impairment in social interaction, deviance in communication, and repetitive behaviors. Dysfunctional ionotropic NMDA and AMPA receptors, and metabotropic glutamate receptor 5 activity at excitatory synapses has been recently linked to multiple forms of ASD. Despite emerging evidence showing that d-aspartate and d-serine are important neuromodulators of glutamatergic transmission, no systematic investigation on the occurrence of these D-amino acids in preclinical ASD models has been carried out.

METHODS

Through HPLC and qPCR analyses we investigated d-aspartate and d-serine metabolism in the brain and serum of four ASD mouse models. These include BTBR mice, an idiopathic model of ASD, and Cntnap2^-/-, Shank3^-/-, and 16p11.2^+/- mice, three established genetic mouse lines recapitulating high confidence ASD-associated mutations.

RESULTS

Biochemical and gene expression mapping in Cntnap2^-/-, Shank3^-/-, and 16p11.2^+/- failed to find gross cerebral and serum alterations in d-aspartate and d-serine metabolism. Conversely, we found a striking and stereoselective increased d-aspartate content in the prefrontal cortex, hippocampus and serum of inbred BTBR mice. Consistent with biochemical assessments, in the same brain areas we also found a robust reduction in mRNA levels of d-aspartate oxidase, encoding the enzyme responsible for d-aspartate catabolism.

CONCLUSIONS

Our results demonstrated the presence of disrupted d-aspartate metabolism in a widely used animal model of idiopathic ASD.

GENERAL SIGNIFICANCE

Overall, this work calls for a deeper investigation of D-amino acids in the etiopathology of ASD and related developmental disorders.

Blood platelet research in autism spectrum disorders: In search of biomarkers

Autism spectrum disorder (ASD) is a clinically heterogeneous neurodevelopmental disorder that is caused by gene-environment interactions. To improve its diagnosis and treatment, numerous efforts have been undertaken to identify reliable biomarkers for autism. None of them have delivered the holy grail that represents a reproducible, quantifiable, and sensitive biomarker. Though blood platelets are mainly known to prevent bleeding, they also play pivotal roles in cancer, inflammation, and neurological disorders. Platelets could serve as a peripheral biomarker or cellular model for autism as they share common biological and molecular characteristics with neurons. In particular, platelet-dense granules contain neurotransmitters such as serotonin and gamma-aminobutyric acid. Molecular players controlling granule formation and secretion are similarly regulated in platelets and neurons. The major platelet integrin receptor αIIbβ3 has recently been linked to ASD as a regulator of serotonin transport. Though many studies revealed associations between platelet markers and ASD, there is an important knowledge gap in linking these markers with autism and explaining the altered platelet phenotypes detected in autism patients. The present review enumerates studies of different biomarkers detected in ASD using platelets and highlights the future needs to bring this research to the next level and advance our understanding of this complex disorder.