Pre‐natal brain development as a target for urban air pollution

Abstract

Air pollution is the main urban‐related environmental hazard and one of the major contributors to the global burden of disease based on its cardiovascular‐respiratory impacts. In children, exposure to urban air pollution is associated, among others, with decelerated neurodevelopment early in life and increased risk of neurodevelopmental problems such as attention‐deficit hyperactivity disorder, autism spectrum disorders, academic failure and the start of Alzheimer's pathogenesis. However, the evidence of the effects of air pollution on brain development is still inadequate, mainly due to the limitations in (a) characterizing brain development (most studies were based on subjective tools such as questionnaires or neuropsychological tests) and (b) air pollution exposure (most studies only used residential levels based on geographical modelling and also overlooking the variation in the mixture of air pollutants as well as the composition and hence toxicity of particulate pollutants in different settings), (c) the lack of studies during the most vulnerable stages of brain development (foetal and early life (first two years post‐natally)) and (d) the lack of structural and functional imaging data underlying these effects. In mice, in utero exposure to fine particles was linked to structural brain changes and there is a need to establish the generalizability of these findings in human beings. Though scarce, current evidence in children supports the importance of the pre‐natal period as a susceptible window of exposure. Two studies in schoolchildren found that pre‐natal air pollution exposure might damage brain structure while exposure during childhood was not linked to any structural alteration. Another study showed that children with higher traffic‐related air pollution at school had lower functional integration in key brain networks, but no changes in brain structure, possibly partly because of the time window of air pollution exposure (in utero versus childhood exposure). A key development is to discover the windows of greatest sensitivity of structural brain changes to air pollution exposure by incorporating the recent advances in non‐invasive imaging to characterize natal and post‐natal brain development and exploring whether and to what extend placental dysfunction could mediate such an association. Studying pre‐natal life is important because effects at this time are of a potentially irreversible nature and because the largest preventive opportunities occur during these periods.

Reduced gray matter volume and cortical thickness associated with traffic-related air pollution in a longitudinally studied pediatric cohort

“…Placental expression of brain-derived neurotrophic factor (BDNF) and synapsin 1 (SYN1), two genes implicated in normal neurodevelopmental trajectories, decreased with increasing in utero exposure to PM 2.5 [68]. Direct or indirect maternal effects from air pollution, such as systemic low-grade inflammation, increased plasma viscosity, hormonal disruption or epigenetic changes, potentially impair placenta function and lead to neurological disruption by time of birth via mechanisms from decreased oxygen and nutrient transport [69].…”

Associations between solid fuel use and early child development among 3 to 4 years old children in Bangladesh: Evidence from a nationally representative survey

“…However, most of these studies are limited to developed countries (15,20). Recent evidence suggests that about 25 million children under 5 in LMICs are at risk of not reaching their full potential due to poverty, stunting, nutrient deficiency, violence, heavy metal exposure, and other social, biological, and physiological factors (24,25).…”

Translocation of (ultra)fine particles and nanoparticles across the placenta; a systematic review on the evidence of in vitro, ex vivo, and in vivo studies

“…Such in utero exposure may not only influence fetal development and induce adverse pregnancy outcomes, but it can also adversely affect health in later life since the etiology of diseases in adulthood may have a fetal origin [ 2 ], as postulated in the Developmental Origins of Health and Disease hypothesis [ 3 ]. Various epidemiological studies identified associations between prenatal exposure to (ultra)fine particles and adverse health outcomes (i) at birth including an increased risk of low birth weight (< 2500 g) [ 4 , 5 ] and preterm birth (< 37 weeks of gestation) [ 6 , 7 ], and (ii) later in life such as cardiovascular disease [ 8 , 9 ], respiratory problems [ 10 , 11 ], and neurodevelopmental alterations [ 12 , 13 ]. (Ultra)fine particles refer to the particles that are incidentally generated and emitted in the (outdoor) air, often as by-products of fossil fuel combustion or industrial emission.…”