A reply to 'Metabolic effects of sapropterin treatment in autism spectrum disorder: a preliminary study'

Brain Opioid Activity and Oxidative Injury: Different Molecular Scenarios Connecting Celiac Disease and Autistic Spectrum Disorder

Celiac Disease (CD) is an immune-mediated disease triggered by the ingestion of wheat gliadin and related prolamins from other cereals, such as barley and rye. Immunity against these cereal-derived proteins is mediated by pro-inflammatory cytokines produced by both innate and adaptive system response in individuals unable to adequately digest them. Peptides generated in this condition are absorbed across the gut barrier, which in these patients is characterized by the deregulation of its permeability. Here, we discuss a possible correlation between CD and Autistic Spectrum Disorder (ASD) pathogenesis. ASD can be induced by an excessive and inappropriate brain opioid activity during the neonatal period. Cereal-derived peptides produced in celiac patients cross the blood–brain barrier and bind to endogenous opioid receptors interfering with neurotransmission and generating deleterious effects on brain maturation, learning and social relations. Moreover, an increase in oxidative stress and a decrease in the antioxidant capacity, as well as an extended mitochondrial impairment in the brain, could represent a possible connection between ASD and CD. Therefore, we critically discuss the proposed relationship between ASD and CD and the possible usefulness of a gluten-free diet in ASD patients.

Speech-Stimulating Substances in Autism Spectrum Disorders

Autism spectrum disorder (ASD) is characterized by the core domains of persistent deficits in social communication and restricted-repetitive patterns of behaviors, interests, or activities. A heterogeneous and complex set of neurodevelopmental conditions are grouped in the spectrum. Pro-inflammatory events and immune system dysfunctions are cellular and molecular events associated with ASD. Several conditions co-occur with ASD: seizures, gastro-intestinal problems, attention deficit, anxiety and depression, and sleep problems. However, language and speech issues are key components of ASD symptoms current therapies find difficult to face. Several speech-stimulating substances have been shown to be effective in increasing speech ability in ASD subjects. The need for large clinical trials to determine safety and efficacy is recommended.

Environmental factors influencing the link between childhood ADHD and risk of adult coronary artery disease

Yorbik et al. reported novel findings regarding a hypothesized relationship between childhood attention-deficit hyperactivity disorder (ADHD) and later risk for coronary heart disease in adulthood. The authors found that mean platelet volume (MPV), a marker of platelet reactivity and a presumable biomarker in patients with cardiovascular disease, was significantly elevated in children with ADHD compared to healthy controls. The mechanistic importance of this novel discovery remains unknown and warrants clarification. We have made the novel proposition that environmental exposure to the agricultural and combustion air pollutant, nitrous oxide (N₂O), may be an etiological contributor to neurodevelopmental disorders. Clinical studies suggest that N₂O may enhance platelet hyperaggregation, possibly via its biphasic role as an MAO inhibitor especially at trace levels of exposure or via the generation of oxidative stress. Therefore, this correspondence briefly details the hypothesis that altered biochemical profiles in neurodevelopmental disorders, derived from chronic environmental exposure to the agricultural and combustion air pollutant, N₂O, may promote coronary artery disease in adulthood.

Zinc and Copper Metabolism and Risk of Autism: a reply to Sayehmiri et al

OBJECTIVE

Sayehmiri et al. recently conducted a meta-analysis to explore the relationship between zinc and copper metabolism and autism spectrum disorders (ASD). Recent reports have elucidated a full behavioral profile of mice exposed to prenatal zinc deficiency and documented a phenotype similar to that found in autism spectrum disorders (ASD). These studies suggest that significant alterations in Zn metabolism may be an important nutritional component in the development of ASD.

MATERIALS & METHODS

The idea that prenatal zinc deficiency may be to blame is cursorily challenged. Epidemiological studies show that high-income countries with a low estimated prevalence of inadequate zinc intake report the highest prevalence of ASD. Consistent with other reports indicating a link between air pollution and ASD, it has recently been proposed that use of the herbicide, glyphosate, in agriculture may serve as an instrumental variable in predicting later neurodevelopmental impairment via emissions of the agricultural air pollutant, nitrous oxide (N2O).

RESULTS

Work in anesthesiology has demonstrated the neurological effects from subanesthetic doses of N2O, including its inhibition of the alpha 7 nicotinic acetylcholine receptor (α7), a receptor coupled to both central nitric oxide (NO) metabolism and peripheral anti-inflammation.

CONCLUSION

This correspondence explores how the aforementioned nutritional phenotypes found by Sayehmiri et al. in their systematic review may be a compensatory mechanism to counter the effects (namely, α7 inhibition) of air pollutant exposures occurring during the most critical stages of fetal development.

Environmental factors in the development of autism spectrum disorders: A reply to Sealey et al. (2016)

Sealey et al. have reviewed the available evidence on environmental factors that may predispose the development of autism spectrum disorders (ASD) in vulnerable populations. The authors identify exposure to vaccines, pesticides, and air pollutants as potential contributors. The author of this correspondence has previously proposed elsewhere that exposure to increasing levels of the agricultural and environmental pollutant, nitrous oxide (N2O), may be the dominant etiology of ASD and other neurodevelopmental disorders. N2O is thought to target the opioidergic system, including the Ƙ-opioid receptor (KOR). Exposure to thimerosal-containing vaccines may disrupt the activity of several endogenous targets as has been shown, principally including μ-opioid receptor (MOR). Given the antagonistic actions of the MOR and KOR, dysregulation of MOR may leave the heightened dynorphin/KOR system unchecked, possibly inducing a negative emotional state that is characteristic of ASD. Future attention may need to be focused on understanding on how early-life mercury exposures, such as in vaccines, may or may not reveal a gestational opiate dependence induced from other ASD-implicated environmental factors.

Does environmental exposure to the greenhouse gas, N2O, contribute to etiological factors in neurodevelopmental disorders? A mini-review of the evidence

BACKGROUND

Neurodevelopmental disorders are increasing in prevalence worldwide. Previous work suggests that exposure to the environmental air pollutant and greenhouse gas - nitrous oxide (N₂O) - may be an etiological factor in neurodevelopmental disorders through the targeting of several neural correlates.

METHODOLOGY

While a number of recent systematic reviews have addressed the role of general anesthesia in the surgical setting and neurodevelopmental outcomes, a narrative mini-review was conducted to first define and characterize the relevant variables (i.e., N₂O, attention-deficit hyperactivity disorder [ADHD] and autism spectrum disorders [ASD]) and their potential interactions into a coherent, hypothesis-generating work. The narrative mini-review merges basic principles in environmental science, anesthesiology, and psychiatry to more fully develop the novel hypotheses that neurodevelopmental impairment found in conditions like ADHD and ASD may be due to exposure to the increasing air pollutant, N₂O.

RESULTS

The results of the present mini-review indicate that exposure to N₂O, even at non-toxic doses, may modulate central neurotransmission and target many neural substrates directly implicated in neurodevelopmental disorders, including the glutamatergic, opioidergic, cholinergic, and dopaminergic systems. Epidemiological studies also indicate that early and repeated exposure to general anesthesia, including N₂O, may contribute to later adverse neurodevelopmental outcomes in children.

CONCLUSIONS

The current evidence and subsequent hypotheses suggest that a renewed interest be taken in the toxicological assessment of environmental N₂O exposure using validated biomarkers and psychiatric endpoints. Given the relevance of N₂O as a greenhouse gas, societies may also wish to engage in a more robust monitoring and reporting of N₂O levels in the environment for climactic benefit as well.

Gluten Intolerance and Neurodevelopmental Disorders: Is Nitric Oxide the Common Biomarker Linking These Conditions?

Cruchet et al. attempt to tease out the myths and facts surrounding the growing popularity of certain dietary approaches in the management of neurodevelopmental disorders, like attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorders (ASDs). The authors identify a particular exclusionary-type approach that seeks to eliminate dietary gluten. Although the relationship between celiac disease (CD) and ADHD/ASD is not well established, a repeated clinical feature noted in CD is the elevated levels of nitric oxide in serum and urine. Elevated oxidative stress has also been observed in neurodevelopmental conditions, and the author of this correspondence has been the first to propose that chronic, environmental exposure to the air pollutant, nitrous oxide may contribute to these oxidative stress profiles through neural cholinergic perturbation. Therefore, the purpose of this correspondence is to highlight this biochemical connection between these conditions so as to identify the clinical populations who may realize the greatest benefit of these dietary approaches, while minimizing any potential risk of nutrient deficiencies.