Oxidized casein impairs antioxidant defense system and induces hepatic and renal injury in mice

•Oral oxidized casein causes oxidative stress in liver and kidney.•Oral oxidized casein induces fibrosis in liver and kidney.•Oral oxidized casein modifies the Nrf2–ARE gene pathway in liver and kidney. Oxidized protein products (OPPs) can be easily found in meat and milk during processing and storage. Evidence supports that accumulation of endogenous OPPs plays a negative role in physiological metabolism. However, the impacts of dietary OPPs and the mechanisms have not been elucidated yet. The present study evaluated whether oral oxidized casein would destruct the antioxidant defense system and cause potential oxidized injury in mice liver and kidney. We performed oxidized casein (modified respectively by H2O2–Cu and HClO) feeding experiments using KM mice (20–22g). A 10-weeks feeding of oxidized casein as basal protein caused oxidative stress by increasing protein carbonylation (PC), advanced oxidation protein products (AOPPs), dityrosine (Dityr), lipid peroxidation and ROS levels in mice liver, kidney and blood (P