Cellular antioxidant enzyme activity and biomarkers for oxidative stress are affected by heat stress

Heat stress (HS) causes oxidative stress and cellular changes in an attempt to detoxify the harmful effects of reactive oxygen species (ROS). However, how ROS affect different organs in chickens under acute and chronic HS is relatively unknown. We investigated the cellular enzyme activity and biomarker changes in the liver and Pectoralis (P) major muscle in broiler chickens subjected to both acute and chronic HS. Forty-eight broiler chickens at 14 days old were randomly assigned to either 25 degrees C (control) or 35 degrees C (heat-stressed) for 12 days. Five birds per treatment at 1 and 12 days post-HS were euthanized, and the liver and P. major muscle were sampled. Superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione (GSH), glutathione reductase (GR), glutathione S-transferase (GST) activity as well as 8-hydroxy-2'-deoxyguanosine (8-OHdG), advanced glycation end product (AGE), malondialdehyde (MDA), and protein carbonyl (PCO) were analyzed as biomarkers for DNA, carbohydrate, lipid, and protein oxidation, respectively. The SOD, CAT, and GSH-GPx activity levels in the liver and the P. major muscle changed under HS; however, some of the changes were tissue-specific or dependent on the duration of the HS. There were increased liver 8-OHdG during chronic HS and also increased liver AGE levels during both acute and chronic HS indicating significant carbohydrate and DNA oxidations. In the P. major muscle, we observed significant increases in lipid peroxidation and protein oxidation which may reflect that this tissue is less resilient to oxidative damage under heat stress. We show that heat stress caused tissue-specific changes to levels of oxidation biomarkers in chicken.