Protective effects from Houttuynia cordata against Streptococcus agalactiae-induced liver injury of GIFT Oreochromis niloticus strain

In order to study the effect of Houttuynia cordata planting in ponds on the repair of liver damage of GIFT Oreochromis niloticus caused by Streptococcus agalactiae, H. cordata were planted in culture ponds with 0% (control group), 5%, 10% and 15% of the pond area, respectively. After 90 days of culture, GIFT O. niloticus were artificially challenged by S. agalactiae. The livers were collected at 0, 24, 48 and 72 hours post infection (hpi), and the liver biochemistry, antioxidant activity, histology and HSP 70 expression were studied. The results showed that the activities of ALT and AST in the control group were the highest at 48 and 72 hpi. The activity of ALT in each H. cordata planting group had no significant change before and after infection. At 72 hpi, the activity of AST in 10% group returned to the level before infection. The antioxidant index showed that planting H. cordata could slow down the decrease of T-AOC in liver caused by streptococcal infection. It helps to significantly elevate the activity of antioxidant enzymes in liver, such as SOD, GSH-Px, CAT and NOS, and increase the scavenging ability of free radicals. It also reduced the levels of lipid peroxidation products(MDA). Histopathology showed that the hepatic sinuses in the control group were obviously congested, the hepatic cord was disordered and the hepatocytes were steatosis at 48 hpi, while O. niloticus in all planting H. cordata groups showed only eosinophilia and slight dilatation of hepatic sinuses after infection. The results of quantitative PCR showed that the expression of HSP 70 in the liver of GIFT O. niloticus in each group increased significantly after infection, and the expression of HSP 70 in the control group was significantly higher than that in the H. cordata planting group at each time point after infection. The results showed that H. cordata planting markedly protected liver against subsequent S. agalactiae-induced oxidative and inflammatory injury via slowing the rise of ALT and AST, increasing activity of antioxidant enzymes. It effectively reduce the pathological damage caused by streptococcal infection. GIFT O. niloticus promoted the early repair and degradation of damaged protein through the high expression of HSP 70. Planting H. cordata has anti-inflammatory effect and improves the ability of fish to resist pathogenic bacteria.