Quinoxaline 1,4-dioxides (QdNOs) derivatives, the potent synthetic antibacterial group used in food-producing animals, are assumed to have pro-oxidant properties. However, how oxidative stress mediated their adrenal toxicity is far from clear. The aim of this study was to assess the ability of three QdNOs, i.e. olaquindox (OLA), mequindox (MEQ), and cyadox (CYA), to produce reactive oxygen species (ROS) and oxidative cell damage in porcine adrenocortical cells. Multiple approaches such as cell activity assay, biochemical detectation, flow cytometry and fluorescent were used to study the integrated role of ROS homeostasis, mitochondrial redox metabolism and cell apoptosis as well as chemical stability of these drugs. The results showed that OLA and MEQ treatment evoked a significant dose and time-dependent cell damage in adrenocortical cells, well CYA displayed much less toxicity. As for the intracellular ROS production, OLA irritated a persistent and utmost release of ROS while MEQ made a similar but weaker reaction. CYA, however, had a short and unstable release of intracellular ROS. On the other hand, quinoxalinine-2-carboxylie acid (QCA), one of the metabolites of OLA and MEQ, did not cause any significant production of ROS and showed relatively lower toxicity than its parents. Moreover, an imbalance in the redox metabolism and mitochondrial membrane damage has been implicated in adrenal toxicity of QdNOs. ROS scavengers partially reversed QdNOs-induced mitochondrial damage, indicating that mitochondria may be a major target and critical for ROS-mediated cell death. In a word, these results suggested that ROS is a key mediator of QdNOs-induced cell death via mitochondria-dependent pathway in adrenocortical cells. The results provide a mechanism approach in understanding the characterize of adrenal damage caused by QdNOs in vitro, which would in turn, help in designing the appropriate therapeutic strategies of these kind of feed additives.
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