Thymol exposure mediates pro-oxidant shift by regulating Nrf2 and apoptotic events in zebrafish (Danio rerio) embryos

The biochemical process of oxidative stress is an integral mechanism of chemical toxicity, contributing to complex pathological disorders. Thymol (THY) has a wide range of therapeutic applications for several ailments, although a better understanding of signaling cues regulated by this compound is needed to address the mechanism of its action. To better perceive the mode of action, we investigated the potential impact of THY on zebrafish embryos, with special emphasis on ROS biogenesis. In this study, we exposed the zebrafish embryos to 25, 50 and 100 mu M of THY for 96 hours post fertilization (hpf). Noticeable teratogenic effects were observed upon assessing the survival rate (LC50 = 42.35 mu M), hatching process, morphological exam and cardiac functions, thereby verifying the toxicity of THY on zebrafish embryos. Furthermore, we analyzed the effect of THY on the levels of ROS, mitochondrial membrane potential (Delta Psi m) and immunofluorescence by DCFH-DA, JC-1, Casp-3FITIC staining, respectively. Furthermore, we preformed the expressional analysis of Nrf2, superoxide dismutase-1 (SOD-1), catalase (CAT), Cytochrome P450 (CYP450) and apoptotic marker proteins (AIF, p53, Bax, Bcl-2, Casp-3 and Casp-9) in zebrafish embryos. As expected, we noticed a significant modulatory effect on the above mentioned activities by THY. Collectively, our findings suggest that ROS might be the prime mediator responsible for THY-induced oxidative damage, thereby affecting the cellular defense mechanism and apoptotic events in zebrafish embryos.