Ketamine-induced oxidative stress at different developmental stages of zebrafish (Danio rerio) embryos†
Ketamine, a widely used anesthetic in a variety of species, has been shown to exert a potential teratogenic effect during the early life stages of zebrafish. A number of mechanisms have been suggested for the etiology of teratogens. One of the most studied involves reactive oxygen species (ROS) formation and oxidative damage. In this study, zebrafish embryos were used to analyze oxidative stress as a potential mechanism of ketamine-induced toxicity. The changes in the accumulation and in vivo patterns of ROS, enzymatic activities (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), lactate dehydrogenase (LDH) and acetylcholinesterase (AChE)), glutathione levels (oxidized (GSSG) and reduced (GSH)), oxidative damage (lipid peroxidation (LPO) and protein carbonyls (CO)) and gene expression (gclc, gstp1, sod1 and cat) were evaluated at 8 and 24 hours post fertilization (hpf) in zebrafish embryos exposed during 20 minutes to 0.2, 0.4 and 0.8 mg mL−1 ketamine in the course of blastula (2.5 hours post fertilization-hpf), gastrula (5.5 hpf) and segmentation (10.5 hpf). Although no changes in ROS patterns were visible after all ketamine exposures, an increase in GSH levels was observed after exposure during blastula, indicating possible alterations in cell oxidative capacity. After exposure in gastrula, an increase in SOD and CAT enzymatic activities along with an increase in GSSG levels were observed at 8 hpf. At 24 hpf, CAT activity remained higher in ketamine exposed groups. The expression of the cat gene was also augmented at this time point. The changes were related with the ability of the embryo to handle oxidative stress and to a turning point during development of the oxidative defense system. At segmentation, the exposure to ketamine induced changes in the accumulation of ROS and sod gene expression which were related to protective mechanisms against ketamine-induced oxidative stress. Changes in acetylcholinesterase were also observed which may be related to changes in ROS. The overall results show that ketamine induces phase-dependent oxidative stress misregulation that could be the key factor for ketamine toxicity and could help to elucidate and provide more information on the mechanism of embryotoxicity of ketamine.