Low-level pyrene exposure causes cardiac toxicity in zebrafish (Danio rerio) embryos

It is widely accepted that the most abundant polycyclic aromatic hydrocarbons (PAHs) in weathered crude oils is cardiotoxic. Although PAHs toxic endpoints show strong correlation with the aryl hydrocarbon receptor (AhR), a ligand activated transcription factor, and is thought to be a potent inducer of cytochrome P4501A, the action mechanism of PAHs on vertebrate cardiovascular development and disease is unclear. Herein, we address the cardiac developmental effects of exposure to the weak AhR agonist pyrene on the early life-stages of zebrafish. Embryos were exposed to 0, 0.05, 0.5, 5, and 50 nmol/L pyrene up to 72h post-fertilization (hpf). Pyrene-treated embryos showed dose-dependent heart abnormalities, such as pericardial edema and cardiac looping defects. Changes in AhR1a, AhR1b, AhR2, and Cyp1A expression were assessed by real-time RT-PCR. The results showed that low-level pyrene failed to alter these genes expression. However, the homeodomain transcription factor Nkx2.5, which plays an essential role in the development of the cardiovascular system, was down-regulated in a dose-dependent manner by pyrene exposure. The bone morphogenetic protein 2b (Bmp2b), which has been identified as the upstream gene of Nkx2.5, also was inhibited in a dose-dependent manner after treatment with pyrene. Taken together, these data indicated that embryonic exposure of zebrafish to low-level environmental pyrene disrupt normal cardiac development and alter expression of defective cardiac differentiation related genes.