Effects of increasing dietary zinc oxide levels on the hepatic mitochondrial energy metabolism, oxidative balance and antioxidant system in weaned piglets

This study compared different levels of dietary zinc oxide (ZnO) on mitochondria ATP synthesis and the cellular and systemic redox balance in weaned pigs. One hundred twenty weaned piglets (7.96 ± 1.17 kg, 21 days of age) were randomly allocated in one of three diets containing different Zn levels (as ZnO); 100 (100Zn), 1000 (1000Zn) and 3000 mg/kg (3000Zn), and were slaughtered at day 21, 23, 35 or 42 for the collection of blood and liver samples. Dietary copper (Cu) levels were constant at 131 mg/kg. Hepatic mitochondrial concentrations of Zn and Cu, hepatic mitochondria respiration, antioxidant response and the hepatic expression of related genes were analyzed. Piglets fed 3000Zn had the highest Zn (P < 0.01) and the lowest Cu concentrations (P = 0.01) in hepatic mitochondria. The hepatic oxygen consumption rate for maximal respiration was the highest in 3000Zn piglets (P < 0.05) whereas hepatic cytochrome c oxidase activity tended to be lower (P = 0.06) and intracellular ATP concentrations was the lowest (P = 0.01). Mitochondrial Cu/Zn superoxide dismutase (Cu/Zn-SOD) activity was the lowest (P < 0.01) and glutathione peroxidase (GPx) activity tended to be the lowest (P = 0.07) for 3000Zn piglets. The mRNA expression of the antioxidant related genes copper chaperone for superoxide dismutase (CCS) was highest (P = 0.01) in 3000Zn piglets and tended to be the highest (P = 0.07) for glutathione synthetase (GSS). Plasma carbonyls concentrations (P = 0.02) and GPx activity (P = 0.01) were the highest while SOD activity was not impacted (P = 0.55) in 3000Zn piglets. In conclusion, supplementing 3000 mg Zn/kg had detrimental impacts on mitochondria Zn and Cu homeostasis, resulting in a dysfunctional mitochondria respiratory chain and disturbed antioxidant response in post-weaning piglets.