Soybean glycinin caused NADPH-oxidase-regulated ROS overproduction and decreased ROS elimination capacity in the mid and distal intestine of juvenile grass carp (Ctenopharyngodon idella)

Soybean glycinin could increase reactive oxygen species (ROS) content and cause damage in the intestine of Jian carp. However, related mechanisms are largely unknown. To WA the hypothesis that glycinin increases intestinal ROS content by increasing ROS generation and decreasing ROS elimination capacity, juvenile grass carp (Ctenopharyngodon idella) were distributed into 3 treatments, fed with control, 8% glycinin or 8% glycinin + 1.2% glutamine diets for 7 weeks, and intestinal oxidative damage, ROS content, intestinal ROS generation and elimination parameters were measured. Compared with control treatment, fish fed with glycinin diet had higher ROS, protein carbonyl (PC) and malondialdehyde (MDA) in the mid intestine (MI) and distal intestine (DI) (P < 0.05) rather than proximal intestine (PI) (P >= 0.05). For ROS generation parameters, compared with control treatment, dietary glycinin increased NADPH oxidase (NOX) activities, NOX1 and NOX2 protein abundance, and NOX1, NOX2, NOX organizer (NOXO) 1b, NOX activator (NOXA) 1, p47phox and p67phox mRNA abundance (P < 0.05) of MI, increased NOX activities, NOX1 protein, NOXO1b, NOXA1 and p22phox mRNA abundance (P < 0.05) of DI, and decreased NOX activities and all the mRNA abundance of NOX family genes measured (P < 0.05) except NOX4, NOX01a and p47phox in the PI (P >= 0.05). For ROS elimination parameters, compared with control treatment, dietary glycinin decreased total and nuclear Nrf2 protein abundance, total antioxidant capacity (T-AOC), anti-superoxide anion (ASA), anti-hydroxy radical (AHR), CuZn-SOD, catalase, glutathione (GSH) peroxidase (GPx), GSH-S-transferase (GST) and GSH reductase (GR) activities of MI (P < 0.05), total and nuclear Nrf2 protein abundance, T-AOC, ASA, AHR, CuZn-SOD, Mn-SOD, CAT, GPx and GST activities (P < 0.05) of DI and T-AOC, ASA, CuZn-SOD, Mn-SOD and catalase activities (P < 0.05) of PI. Compared with glycinin treatment, glycinin + glutamine treatment decreased ROS, PC and MDA of MI (P < 0.05) but neither in PI nor DI of grass carp (P >= 0.05). Concluded, this study showed that (1) glycinin increased ROS generation related to NOX signaling pathway and decreased ROS elimination capacity related to the Nrf2 translocation in the MI and DI, which lead to the increased ROS content; (2) glycinin decreased both ROS generation and ROS elimination capacity in the PI of fish, which lead to the unchanged ROS content; (3) Glutamine could protect glycinin-induced oxidative stress mainly in the MI.