Comparative mechanistic study of developmental neurotoxicity of organophosphorus pesticides - Organophosphorus pesticides (OPs), a large and chemically diverse class, are the most commonly used and
economically important insecticides worldwide, accounting for approximately 40% of recently used insecticides
in the U.S. While legal OP concentrations are not acutely toxic to humans, studies suggest that chronic prenatal
and infant exposures can lead to life-long neurological damage and behavioral disorders. Acute OP poisoning
due to inhibition of acetylcholinesterase (AChE) is well-understood. But, despite decades of OP research, it
remains debated whether and how subacute OP exposure at regulated levels that do not significantly inhibit
AChE damages the developing human brain. Much of this controversy is because connections between target
molecules/pathways and adverse health outcomes are largely unknown since organismal screening in mammals
that could yield these connections is extremely slow and expensive. Thus, there is a critical need for high-
throughput (HT) non-mammalian organismal screening to fill this knowledge gap. Additionally, humans often
encounter several OPs simultaneously, due to their ubiquity and frequent use in mixtures. Thus, it is imperative
to understand the toxicity mechanisms of different OPs individually and in combinations to unravel possible non-
additive toxic effects and to accurately predict toxicity of combinatorial exposure to humans. The overarching
goal of this research is to reveal the mechanisms underlying DNT of OPs and OP mixtures, to inform prenatal
OP exposure guidelines. The specific objective is to use comparative OP HT screening in planarians to test
the hypothesis that phenotypic differences associated with OP DNT are due to interactions with different
molecular targets. Findings from the PI’s ongoing R15 using automated behavioral screening in the asexual
freshwater planarian Dugesia japonica support this hypothesis. Subchronic exposure to 7 OPs produced different
phenotypes that could not be explained by levels of AChE inhibition. Five of these OPs produced robust
behavioral defects in regenerating planarians at sublethal concentrations. The proposed work builds upon these
results to determine the mode of action of these 5 OPs. The hypothesis will be tested by investigating the
developmental periods most vulnerable to OP exposure using a tiered screening approach (Aim 1) and by
identifying which molecular pathways within these periods are affected using whole transcriptome RNA
sequencing (Aim 2). The proposed project is innovative, because it is the first study that combines state-of-the-
art behavioral HT screening, cellular / neuroanatomical studies, and transcriptomics to unravel the mechanisms
of DNT of multiple OPs and establish connections between disrupted neurodevelopmental processes and
organismal adverse outcomes. This mechanistic understanding will provide a framework to unravel the
mechanisms of multi-OP interactions in future studies. Toxicity pathways identified in planarians can be used to
guide targeted mechanistic studies in mammalian systems, dramatically speeding up the testing pipeline and
allowing for the translation of these results to human health.
