Quinocetone-induced Nrf2/HO-1 pathway suppression aggravates hepatocyte damage of Sprague-Dawley rats

Quinocetone (3-methyl-2-quinoxalin benzenevinylketo-1,4-dioxide, QCT) is a widely used veterinary drug in PR China that promotes feed efficiency and growth of various animals. However, its potential toxicity has been concerned recently. In the present study, we investigated QCT-induced hepatocyte changes and its related mechanism, especially the expression of Nrf2/HO-1 pathway. Oxidative stress induced by QCT in hepatocyte led to DNA damage, inflammation and apoptosis. Nevertheless, hepatocyte has a self-repair system to protect itself from oxidative stress. In the 50 mg/kg/day QCT group, the morphology and function of liver were approximately maintained on normal level, which indicated that the damaged cell might have a self-repair mechanism. Notably, nuclear factor-erythroid 2-related factor 2/heme oxygenase-1 (Nrf2/HO-1) pathway plays a critical role in protecting cells against reactive oxygen species (ROS) generation. However, higher doses of QCT (800 mg/kg/day and 2400 mg/kg/day) inhibited the expression of Nrf2/HO-1 pathway, which resulted in excessive ROS generation and irreversible oxidative DNA damage, inflammation and apoptosis. In conclusion, although QCT-induced oxidative stress activates the expression of Nrf2/HO-1 pathway initially, persistent QCT exposure will inhibit this expression and aggravate hepatocyte damage. Simultaneously, inflammation and apoptosis continues to progress, liver dysfunction and tissue damage will be occurred eventually.