Neurotoxicants Are in the Air: Convergence of Human, Animal, andIn VitroStudies on the Effects of Air Pollution on the Brain

Abstract

In addition to increased morbidity and mortality caused by respiratory and cardiovascular diseases, air pollution may also negatively affect the brain and contribute to central nervous system diseases. Air pollution is a mixture comprised of several components, of which ultrafine particulate matter (UFPM; <100 nm) is of much concern, as these particles can enter the circulation and distribute to most organs, including the brain. A major constituent of ambient UFPM is represented by traffic-related air pollution, mostly ascribed to diesel exhaust (DE). Human epidemiological studies and controlled animal studies have shown that exposure to air pollution may lead to neurotoxicity. In addition to a variety of behavioral abnormalities, two prominent effects caused by air pollution are oxidative stress and neuroinflammation, which are seen in both humans and animals and are confirmed by in vitro studies. Among factors which can affect neurotoxic outcomes, age is considered the most relevant. Human and animal studies suggest that air pollution (and DE) may cause developmental neurotoxicity and may contribute to the etiology of neurodevelopmental disorders, including autistic spectrum disorders. In addition, air pollution exposure has been associated with increased expression of markers of neurodegenerative disease pathologies.

Neurological Disorders from Ambient (Urban) Air Pollution Emphasizing UFPM and PM2.5

“…In recent times, studies [4] have shown the negative impacts of ambient air pollution on the brain and central nervous system (CNS) that do not seem to have gained serious attention of the researchers. The polluted air is a complex mixture of several components comprising gaseous compounds and particulate matters.…”

“…The third important source in this category includes vapors emitting from building materials, household cleaning, and maintenance gadgets as well as furnishings. The PM and ground level ozone among others are emerging as growing risk of urban human health arising from air pollution [1,4,[7][8][9][10].…”

“…As a result, these particles comprise both organic and inorganic compounds, such as ammonium compounds, carbon, sulfates, nitrates, lipo-polysaccharides, metals, and water. Major sources of PM 2.5 are emissions from automobiles, fuel combustion during cooking at home as well as at roadside eateries, open burning of garbage (municipal solid waste, MSW), industrial activities (petroleum oil refineries, metal processing facilities, power plants), and wildfires [1,4,[7][8][9][10].…”

“…They can carry soluble organic compounds, PAHs, PCBs including dioxins, furans, and oxidized transition metals on their surfaces [1,4,[7][8][9][10]. Thus, UFPM, therefore, assumes considerable importance in studies of neurological disorders from air pollution both in the form of particulate phase as well as gaseous (molecular) phase.…”

“…Interestingly, an estimate indicates that the air pollution ranks among the top ten leading risk factors for mortality that is incidentally responsible for deaths of about 3 million people each year [4]. The global air pollution is contributed from traffic-related urban air pollution in which the diesel exhaust (DE) constitutes the important component [11].…”