The use of nanoparticles in human activities has increased. Therefore, study of the biological effects of different nanoparticles and nanocomposite materials, specially their effects on human and animal organs need special attention. The primary concern is the toxicity of nanoparticles in humans and the potential risk of nanoparticles and their related products on human health. Copper nanoparticles are widely synthesized and used as metal catalyst, heat transfer fluids in machine tools, semiconductors, and even in antibacterial medications, etc. The present investigation was carried out on forty apparently healthy mature westar rats weighing between 120-200 gm with average three months age. The rats were obtained from laboratory animal unite in the faculty of pharmacy, King Saud University and were divided randomly into four groups (10 rats/ group). Group I (G1) was kept as a control and fed with a basal diet without CuO NPs for 9 days. Group II (G2)was obtained CuO NPsin a dose 5 mg/ kg body weight, Group III(G3)was obtained CuO NPsin a dose 10 mg/ kg body weight and Group IV(G4)was obtained CuO NPsin a dose 25 mg/ kg body weight. All treated groups obtained CuO NPs by intraperitonealinjection for 9 days. At the end of experiment, cervical dislocation of rats and the livers were taken for the histological studies. The histopathologicalfinding of G1 revealed normal histological structure of all hepatic tissues without any abnormalities. Meanwhile, G2 and G3 clarified mild to moderate necrosis of the hepatocytes, disorganization of the hepatic cords, microvesicularsteatosis, moderate sinusoidal dilatation with congestion and inflammatory cells infiltration with fibrous tissue proliferation. With Prussian blue reaction, the G2 was observed devoid of any hemosiderin pigments precipitation within the hepatocytes but G3 clarified moderate hemosiderin pigments precipitation. On the other hand, liver of G4 showed sever necrosis of the hepatic parenchyma with loss of all hepatic architectures, inter hepatocellular bleeding, severe steatosis, sever sinusoidal dilatation with congestion accompanied by Kupffer cells hyperplasia and sever lymphocytes aggregation within the hepatic parenchyma. With Prussian blue reaction, sever hemosiderin pigments precipitation within the hepatic tissue was recognized. The present investigation was concluded that the CuO NPs have potential oxidative stress in the hepatic tissues that may affect the function of the liver.
