Adolescent Insecticide Exposure and ADHD Risk: Mechanisms of Immediate Effects and Long-term Vulnerability - Project Summary/Abstract Adolescent brain development is sensitive to exposures and has impacts on neurobehavioral functioning. Insecticide exposure may impact executive and attentional brain circuits which mature during adolescence due to pubertal hormonal influences and these changes may manifest as ADHD-related symptoms. There are gaps in knowledge about how insecticide exposure affects the adolescent brain, when neurobehavioral vulnerability can undermine lifelong relationships, economic attainment, and overall health. While most general populations, including adolescents, are exposed to low levels of insecticides through non- agricultural uses and consuming fruits and vegetables, occupational populations are known to have substantially higher levels of exposure. Therefore, we have worked extensively with a cohort of Egyptian adolescent pesticide- applicators who are occupationally exposed to insecticides (α-cypermethrin and chlorpyrifos). Increased ADHD symptoms and altered neurobehavioral performance in this cohort correlate with α-cypermethrin and chlorpyrifos toxicological burden. However, moderators and mechanisms underlying these associations remain undefined. Our pilot data indicate that combined adolescent exposure leads to altered neurobehavior and dopamine systems in the brain in mice. The effects in pesticide applicators are present many months after exposure. The epigenome is a potential mediator of the relationship between exposures and long-term neurobehavioral effects due to its unique sensitivity to the environment and potential to regulate gene expression throughout the lifespan. Our overall hypothesis is that combined adolescent insecticide exposures impact neurobehavioral outcomes. We additionally hypothesize that effects are modified by testosterone level, act via oxidative stress in dopamine neurons, and have a long-term trajectory via epigenetic change. We will test these with three synergistic aims joining human investigation and animal mechanistic assessments with translation between them, facilitated by a transdisciplinary investigator team, novel approaches, and a well laid-out consortium plan. In Aim 1, we will leverage stored samples and data from adolescent pesticide-applicators to quantify the neurobehavioral impact of combined versus single insecticide exposures, assessing the high- reward, high-risk hypothesis that pesticide-applicator testosterone level moderates this association. In Aim 2, we will model these adolescent insecticide exposures in mice to examine causality and use manipulations to test oxidative stress as a mechanism and testosterone level as a moderator of effects. Cell culture studies will provide convergent results for the role of dopamine neurons. In Aim 3, we will examine DNA methylation across both human and mouse samples collected after completion of peak insecticide exposure, to examine the potential epigenetic mechanisms translationally of long-term neurobehavioral risk. This work is the first step to accelerate translation of scientific research into meaningful improvements in human health— namely improving insecticide exposure policies and developing interventions to protect youth.
