Do Toxic Synergies of Underlying Etiologies Predispose the Positive Association Between Traumatic Brain Injury and ADHD?

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.

Use of anthropogenic nitrogen fertilizers in agriculture is associated with per capita ethanol consumption

It has previously been demonstrated that emissions of the agricultural pollutant, nitrous oxide (N₂O), may be a confounder to the relationship between herbicide use and psychiatric impairments, including ADHD. This report attempts to extend this hypothesis by testing whether annual use of anthropogenic nitrogen-based fertilizers in U.S. agriculture (thought to be the most reliable indicator of environmental N₂O emissions) is associated with per capita ethanol consumption patterns, a behavior often comorbid with ADHD. State estimates of anthropogenic nitrogen fertilizers from the United States Geological Survey (USGS) were obtained for the years between 1987 and 2006. Our dependent variable was annual per capita ethanol consumption. Ethanol consumption was categorized as beer, wine, spirits, and all alcoholic beverages. Least squares dummy variable method using two-ways fixed effects was utilized. Among states above the 50th percentile in farm use of anthropogenic nitrogen for all years (i.e., agricultural states), a one log-unit increase in farm use of anthropogenic nitrogen fertilizers is associated with a 0.13 gallon increase in total per capita ethanol consumption (p<0.0125). No statistically significant association between farm use of anthropogenic nitrogen and per capita ethanol consumption was found in states below the 50th percentile in farm use of anthropogenic nitrogen. The new findings are in agreement with both behavioral human studies demonstrating a link between N₂O preference and alcohol and drug use history as well as molecular studies elucidating shared mechanisms between trace N₂O antinociception and alcohol-seeking related behaviors.

Exposure to ambient PM10 and nitrogen dioxide and ADHD risk: A reply to Min & Min (2017)

Min and Min (2017) conducted an epidemiological investigation that revealed further support of a link between exposure to air pollution and risk for attention-deficit hyperactivity disorder (ADHD) in childhood. We have previously reported that exposure to the agricultural and combustion pollutant, nitrous oxide (N₂O), may be a primary environmental trigger in the onset of neurodevelopmental disorders, like ADHD and autism spectrum disorders. In order to validate our prior work pointing to an association between farm use of nitrogen fertilizers and a severe ADHD phenotype, we have utilized a different statistical approach (i.e., Poisson regression methodology) including two-way fixed effects. The results reported in this correspondence indicate that for a one-log unit increase in the farm use of nitrogen fertilizers, hospitalization risk for ADHD and conduct disorders increases by a factor of 1.16 (p<0.017), which was a statistically significant increase in risk after multiple pollutant comparison correction. Exposure to PM10 and NOx in this analysis was not associated with an increased risk of hospitalization for ADHD and conduct disorder. We are able to validate our prior conclusions and, therefore, suggest that future analyses dedicated to improving the literature on the association between air pollution and risk of ADHD take into account environmental emissions of N₂O.

Gait abnormalities, ADHD, and environmental exposure to nitrous oxide

Papadopoulos et al. (2014) investigated gait profiles of children with attention-deficit hyperactivity disorder-combined type (ADHD-CT) compared to typical developing (TD) controls. The authors reported differences in the gait profile of ADHD-CT in the self-selected fast speed category. Additionally, others have proposed a maturational delay hypothesis in gait, demonstrating that gait variability decreases with age in ADHD children. It has been previously suggested that the cognitive impairment seen in conditions like ADHD may result from chronic, environmental exposure to the air pollutant, nitrous oxide (N2O). Exposure to N2O is thought to exert its antinociceptive properties by stimulating release of dynorphin peptides in the central nervous system which act upon kappa opioid receptors (KOR). Opioid-mediated gait abnormalities in ADHD are supported with evidence that prodynorphin mutations in mice lead to cytotoxic levels of dynorphin A (DYN A) and contribute to abnormal gait profiles and gradual loss of motor coordination. Interestingly, constitutive activity of the KOR receptor in rat brain has been recently shown to undergo maturational alterations, suggesting that while altered gait profiles in ADHD may be a function of the enhanced opioidergic activity attributable to chronic exposure to the environmental air pollutant, N2O, age-attenuated constitutive activity of KOR in brain may explain the normalization of these altered gait profiles in older ADHD subjects.

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.