Developmental pharmacotoxicology in zebrafish (Danio rerio): evaluating the long-term transcriptomic impact of citalopram and opioids

Abstract

The increasing use and environmental detection of neuromodulator pharmaceuticals, particularly opioids and selective serotonin reuptake inhibitors (SSRIs) like citalopram, raises concerns regarding their potential developmental toxicity. The goal of this work was to investigate whether a brief, early developmental exposure to these compounds can result in lasting transcriptomic disruptions. Zebrafish (Danio rerio) were exposed to oxycodone, fentanyl, or citalopram for 2 to 24 hours post-fertilization (hpf), washed, and allowed to develop in toxicant free media until 48 hpf at which point we extracted RNA and performed bulk RNA sequencing to assess persistent gene expression changes. Both studies in this thesis demonstrated that a single, transient exposure during early embryogenesis produced significant and lasting alterations in gene expression. Notably, environmentally relevant concentrations induced a broader transcriptomic response than higher therapeutic concentrations. These findings challenge traditional toxicological assumptions that higher doses yield greater effects. Pathway analysis revealed that both opioids and citalopram disrupted similar biological processes including extracellular matrix organization (ECM), synaptic signaling, and lens development. In opioid- exposed embryos, over-representation analysis identified enrichment in ECM, axon guidance, and synaptic pathways, with particular contributions form collagen and crystallin gene families. Similarly, citalopram exposure led to gene set enrichment of pathways related to synaptic structure, visual system development, metabolic stress responses, and transcriptional regulation. Despite their distinct pharmacological profiles, both opioids and citalopram converged on common developmental targets which may suggest shared vulnerabilities during early neural and visual system development. Thus, even short-term exposures to neuromodulatory pharmaceuticals during critical developmental windows may lead to persistent molecular alterations. This work prompts a need to thoroughly assess large-scale exposure to common toxicants and suggests that low-dose environmental exposures, often regarded as negligible, may exert profound long-term biological impacts.