Researchers Reveal a Link Between Common Air Pollutant and Autism

In healthy amounts, nitric oxide is beneficial to human health, but excessive environmental exposure may be an issue.As scientists work to understand the sharp rise in autism spectrum disorder (ASD) over the last few decades, one likely environmental culprit that has emerged is air pollution.Air pollution may lead to neuroinflammation, a key risk factor in a number of neurological disorders, including autism.In a review published online on Nov. 12 in the journal Brain Medicine, researchers explained that when it comes to the damaging potential of air pollution, a developing brain is at particular risk. During pregnancy, mothers-to-be inhale polluting particles in the air. As these particles make their way through the mothers’ bloodstream, the babies they carry have little defense because the blood-brain barrier of a fetus isn’t developed enough to guard against the polluting influence. The review traces the evidence linking air pollution and autism and suggests new avenues for treatment and diagnosis.Researchers looked at a variety of pollutant particulates and found that smaller particulates, especially PM2.5, were particularly problematic. Tiny particles are able to cross the placenta and affect fetal brain development.Another important finding was that early exposure to nitric oxide—a common component of car exhaust—may also cause problems.Related StoriesThe review’s lead author, Haitham Amal, is an internationally recognized expert in cell signaling and brain disorders. Last year, Amal and his team became the first researchers to establish a link between nitric oxide and autism pathogenesis.Previous research had suggested that nitric oxide exposure could lead to autism. But Amal says these were merely correlation studies. Amal was the first to validate it.“We inhibited the enzymes that produced nitric oxide, and we saw the consequences on the behavioral level. This is the only study in the literature that shows experimentally the link between nitric oxide and autism,” Amal told the Epoch Times.These findings could have implications beyond autism. Amal says nitric oxide shares a molecular mechanism that can impact multiple neurodevelopmental and neurodegenerative diseases.A Closer Look at Nitric OxideNitric oxide is a common air pollutant produced primarily by vehicle emissions and fossil fuel combustion. The toxic effects of inhaling this colorless gas have been known for decades.Nitric oxide is also essential for our health. The body produces its own supply for cardiovascular, respiratory, and immune functions. For people hoping to further enhance these functions, there are supplements and pharmaceuticals available that encourage the body to increase nitric oxide production.“Nitric oxide is a super important molecule, not only in the body but also in the brain. It is involved in synaptic and neuronal function and other processes,” Amal said.However, exposure to nitric oxide in the environment is a different animal. It has been shown to cause oxidative stress, particularly in individuals prone to inflammatory disorders who are believed to be more susceptible to its influence. To identify nitric oxide exposure as a contributing factor in autism, Amal and his team looked at samples from low-functioning children with ASD, transgenic mouse models, and in-vitro human platforms. This data establishes a strong link, but many past findings have already pointed to the connection. Exposure to nitric oxide and its derivative, nitrogen dioxide, during pregnancy and early childhood were previously known to disrupt normal brain development.Researchers suggest that individuals with a genetic predisposition to autism may be more vulnerable to the harmful effects of nitric oxide. Amal and his team posit that mutations in genes that handle oxidative stress and nitric oxide regulation, for example, may increase the inflammatory impact.Limiting ExposureIf nitric oxide exposure is a risk, it makes sense to avoid exposure. Thankfully, there’s less around than there used to be. According to the U.S. Environmental Protection Agency, nitric oxides in the environment have been reduced substantially ever since 1980.Researchers say reducing exposure could play a key role in preventing nongenetic cases of ASD and improving public health outcomes. However, prevention in a particular window of time is crucial.“Exposure to these pollutants during pregnancy and early postnatal development poses a significant risk of ASD since these periods are essential for brain development, including neuronal migration and myelinization,” Amal and his colleagues wrote.Amal is also helping to develop a drug that inhibits nitric oxide. Preclinical work shows a reversal of ASD-like phenotypes when targeting nitric oxide production in animals, and data with human stem cell samples have revealed similar results.“We think that this can be a positive strategy,” Amal said.While the review adds more weight to the idea that air pollution may influence autism