Effects of tetracycline on developmental toxicity and molecular responses in zebrafish (Danio rerio) embryos

The extensive use of pharmaceuticals has resulted in the intensive contamination of water bodies. Tetracycline is a type of antibiotic and its potential toxicity is causing environmental concern. The effects of developmental toxicity and the mechanisms of tetracycline on fish embryos are not well understood. Zebrafish embryos are used in this study to investigate the developmental toxicity of this compound. Four hour post-fertilization (hpf) zebrafish embryos are exposed to different concentrations of tetracycline until 96 hpf. The larvae display developmental delay phenotypes, including hatching delay, shorter body length, increased yolk sac area and uninflated swim bladder upon exposure to tetracycline. Delayed yolk sac absorption and swim bladder deficiency at 96 hpf are observed in the zebrafish larvae upon exposure to 20 μg/L of tetracycline. To test whether tetracycline causes oxidative damage and the resulting oxidative stress-induced apoptosis, the generation of reactive oxygen species (ROS), Acridine Orange staining and real time polymerase chain reaction have been performed in this study. The results indicate that tetracycline exposure results in significant increases in ROS production and cell apoptosis, mainly in the tail areas at 96 hpf. The gene expression pattern demonstrates that tetracycline induces ROS which causes apoptosis in the zebrafish larvae, and the results also indicate that caspase-dependent apoptotic pathways may greatly contribute to tetracycline-induced apoptosis in the early-life stages of the zebrafish. In addition, we have investigated the effects of tetracycline on marker genes related to resistance mechanisms and gene regulating drug biotransformation. The results of these gene expression studies indicate that tetracycline could induce zebrafish to resist pharmaceuticals and Cytochrome P450s that are involved in the biotransformation of tetracycline in zebrafish larvae. The overall results indicate that tetracycline can produce oxidative stress and induce apoptosis, which brings about significant developmental delay in zebrafish embryos.