Effect of dietary protein on the antioxidant capability and inflammatory response in juvenile Chinese soft-shelled turtles (Pelodiscus sinensis) injected with exogenous hydrogen peroxide

This study estimated the influence of dietary protein on the anti-oxidative enzyme activity, mRNA expression of antioxidant-related enzymes, and inflammatory responses in the Chinese soft-shelled turtle ( Pelodiscus sinensis ) when injected with exogenous hydrogen peroxide (H 2 O 2 ). Six diets containing 14.38 %, 20.41 %, 26.19 %, 32.23 %, 37.63 %, and 45.23 % protein were fed to turtles over an 8-week breeding trial, after which the turtles were injected intraperitoneally with H 2 O 2 . High protein diets (≥ 26.19 %) produced the following effects: 1) decreased aspartate aminotransferase and alanine transaminase activities in the serum; 2) decreased lipid peroxidation (ROS and MDA) levels; 3) improved the GSH-PX, SOD, T-AOC, and CAT levels in the liver; 4) activated the nuclear factor erythroid 2-related factor/Kelch-like ECH-associated protein 1 (Nrf2/Keap1) signaling pathway; 5) enhanced the gene expression of CAT , CuZnSOD , MnSOD , Nrf2 , Keap1 , GPX1 , GPX2 , GPX3 , and GPX4 ; 6) repressed the gene expression level of interleukin-1β, interleukin-6, interleukin-8, and tumor necrosis factor alpha; and 7) improved the level of interleukin-10 mRNA. Overall, the results showed that feeding the optimal dietary protein level played a protective role against H 2 O 2 -mediated oxidative damage by regulating the Nrf2 signaling pathway and inflammation. Using broken-line analysis with ALT and AST activities as the evaluation indicators, the optimal dietary protein requirement for the Chinese soft-shelled turtle was estimated to be 25.78 % for ALT and 26.25 % for AST. • Optimal protein ameliorated H 2 O 2 -induced oxidative stress through regulating the Nrf2/keap1 signaling pathway. • Dietary protein decreased lipid peroxidation (ROS and MDA) levels induced by H 2 O 2 . • Optimal protein alleviated H 2 O 2 -induced inflammatory response. • Optimal dietary protein was estimated to be 25.78 % and 26.25 % based on ALT and AST, respectively.