Clinical studies have confirmed that Glycyrrhiza total flavones (GTFs) have good anti-hepatic injury, but whether they have a good protective effect on anti-hepatic injury activity induced by Streptococcus agalactiae in tilapia (Oreochromis niloticus) is unknown. The aims of this study were to investigate the protective effects of Glycyrrhiza total flavones on liver injury induced by S. agalactiae (SA) and its underlying mechanism in fish. A total of 150 tilapia were randomly divided into five groups, each with three replicates containing 10 fish: normal control group, S. agalactiae infection group, and three Glycyrrhiza total flavone treatment groups (addition of 0.1, 0.5, or 1.0 g of GTF to 1 kg of feed). The normal control group was only fed with basic diet, after 60 d of feeding, and intraperitoneal injection of the same volume of normal saline (0.05 mL/10 g body weight); the S. agalactiae infection group was fed with basic diet, and the S. agalactiae solution was intraperitoneally injected after 60 d of feeding (0.05 mL/10 g body weight); the three GTF treatment groups were fed with a diet containing 0.1, 0.5, or 1.0 g/kg of GTF, and the S. agalactiae solution was intraperitoneally injected after 60 d of feeding (0.05 mL/10 g body weight). After 48 h injection, blood and liver tissues were collected to measure biochemical parameters and mRNA levels to evaluate the liver protection of GTFs. Compared with the control group, the serum levels of glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), alkaline phosphatase (AKP) and glucose (GLU) in the streptococcal infection group increased significantly, while the levels of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH) decreased significantly; observations of pathological sections showed obvious damage to the liver tissue structure in response to streptococcal infection. S. agalactiae can also cause fatty liver injury, affecting the function of fatty acid β-oxidation and biosynthesis in the liver of tilapia, and also causing damage to function of the immune system. The addition of GTFs to the diet could improve oxidative stress injury caused by S. agalactiae in tilapia liver tissue to different degrees, promote the β-oxidation of fatty acids in the liver, accelerate the lipid metabolism in the liver, and repair the damaged liver tissue. GTFs have a good protective effect on liver injury caused by streptococcus.
Keywords: Glycyrrhiza total flavones; Streptococcus agalactiae; oxidative stress; tilapia.