Developmental toxicity of hydroxylated chrysene metabolites in zebrafish embryos

One of the primary sources of polycyclic aromatic hydrocarbons (PAHs) in marine environments is oil. Photochemical oxidation and microbial transformation of PAH-containing oils can result in the formation of oxygenated products. Among the PAHs in crude oil, chrysene is one of the most persistent within the water column and may be transformed to 2- and 6-hydroxychrysene (OHCHR). Both of these compounds have been shown to activate (2-OHCHR) and antagonize (6-OHCHR) the estrogen receptor (ER). Previous studies in our lab have shown that estrogen can significantly alter zebrafish development. However, little is known about the developmental toxicity of hydroxylated PAHs. Zebrafish embryos were exposed to 0.5-10 μM of 2- or 6-OHCHR from 2 h post-fertilization (hpf) until 76 hpf. A significant decrease in survival was observed following exposure to 6-OHCHR - but not 2-OHCHR. Both OHCHRs significantly increased the percentage of overall deformities after treatment. In addition to cardiac malformations, ocular and circulatory defects were also observed in embryos exposed to both compounds, while 2-OHCHR generally resulted in a higher prevalence of effect. Moreover, treatment with 2-OHCHR resulted in a significant decrease in hemoglobin levels. ER nor G-Protein coupled estrogen receptor (GPER) antagonists and agonists did not rescue the observed defects. We also analyzed the expression of cardiac-, eye- and circulation-related genes previously shown to be affected by oil. Rhodopsin mRNA expresssion was significantly decreased by both compounds equally. However, exposure to 2-OHCHR significantly increased the expression of the hematopoietic regulator, runx1 (runt related transcription factor 1). These results indicate the toxicity of oxygenated photoproducts of PAHs and suggest that other targets and signaling pathways may contribute to developmental toxicity of weathered oil. Our findings also demonstrate the regio-selective toxicity of hydroxy-PAHs in the effects on eye and circulatory development and raise the need to identify mechanisms and ecological risks of oxy-PAHs to fish populations.