Effect of exogenous hydrogen peroxide on ROS balance and antioxidant response in Chinese soft-shelled turtle Pelodiscus sinensis

Chinese soft-shelled turtle, Pelodiscus sinensis, is an important farmed species in the Southeast Asia and often encounters adverse environmental stresses during cultivation. Knowledge about the stress response, especially antioxidant response, in P. sinensis would help to understand the effect of adverse stress on turtles and to reduce the production loss. In the present study, intraperitoneal injection of H2O2 (0%, 0.3%, 0.6%, and 2.4%) was employed as an exogenous oxidative stressor to directly challenge the antioxidant defense in Chinese soft-shelled turtle, Pelodiscus sinensis, and evaluate the antioxidant capacity and characteristics of antioxidant defense in P. sinensis. Level of reactive oxygen species (ROS), total antioxidant capacity (TAC), antioxidant enzyme activities, ascorbic acid (AA) content and malondialdehyde (MDA) level were measured in the brain, liver, kidney and spleen of P. sinensis at 2 h, 6 h and 24 h post-injection. In general, all cerebral and hepatic parameters did not change, although there were some variations in the liver after 2 h, which recovered after 6 h. In the kidney, only glutathione peroxidase (GPx) activity and AA level increased by 24 h post-injection. Splenic ROS level decreased after 6 h; TAC level and catalase (CAT) activity increased, whereas other antioxidant enzyme activities and AA decreased following by H2O2 injection. Results for MDA level and histology indicated transitory oxidative damage in the liver, but longstanding damage in the spleen. In summary, turtle antioxidant defense work effectively to decrease ROS level even when tissues are faced with intense oxidative stress. However, spleen should be paid more attention because it seemed to be more fragile to intense or long-term oxidative stress than other tissues. Specifically, AA level was important in antioxidant defense of P. sinensis.