Effects of emodin, vitamin C and their combination on biochemical parameters and two HSP70s mRNA expression of Wuchang bream (Megalobrama amblycephala) infected with Aeromonas hydrophila

Abstract

The study aims to evaluate the effects of dietary emodin,high-dose vitamin C(Vc) and their combina-tion on the disease resistance of Wuchang bream(Megalobrama amblycephala) against Aeromonas hydrophila infection.One thousand and two hundred healthy fish with initial body weight of(133.44±2.11) g were selected and randomly divided into four groups: one was the control group fed with basal diet(containing Vc 50.3 mg/kg,with the L-ascorbyl-2-polyphosphate as Vc source);the other three were the treatment groups,fed with basal diets supplemented with emodin 60 mg /kg,Vc 700 mg/kg,and the combination of emodin 60 mg/kg + Vc 700 mg/kg,respectively.After consecutive feeding for 60 days,fifteen fish taken from each tank were intraperitoneally in-fected with A.hydrophila(BSK-10),and the biochemical parameters of serum and liver,the mRNA levels of two heat shock protein 70s(HSP70s) in liver before and after infection were determined.Another ten fish taken from each tank were challenged with A.hydrophila using the same method as above,and the cumulative mortality of each group was counted at different time of post-infection.The results showed that before infection,compared with the control group,serum total protein(TP),lysozyme(LSZ) and alkaline phosphatase(AKP) levels,liver superoxide dismutase(SOD) activity and expression level of inducible HSP70 mRNA significantly increased in emodin and Vc groups,while serum cortisol(COR),triglyceride(TG) and liver malondialdehyde(MDA) contents decreased(P 0.05) in emodin and Vc groups;the liver catalase(CAT) activity also significantly increased in emodin group(P 0.05).Although the serum TP,LSZ and liver HSP70 mRNA levels significantly increased in combination group,and the liver malondialdehyde(MDA) level was also significantly reduced(P 0.05),no syn-ergism was shown. After infection,compared with the control group,the serum TP,LSZ,AKP levels,liver SOD,CAT activities,and the expression levels of HSC70 and HSP70 mRNA increased in emodin and Vc groups in varying degrees,while the serum COR,glucose(GLU),glutamic-pyruvic transaminase(GPT),glutamic-oxaloacetic transaminase(GOT),TG and liver MDA levels were reduced to some extent.In combination group,although these parameters had similar changing trend as the above ones,most of them were not significant different with the control(P 0.05),and also did not show any synergism.Statistic data also showed that after infection with A.hydrophi1a,the cumulative mortalities of emodin and Vc groups were significantly lower than the control group in 24 h and 48 h(P 0.05),but the difference of cumulative mortality between the combination and control groups was not signifi-cant(P 0.05).Thus,the basal diet supplemented with emodin 60 mg/kg or Vc 700 mg/kg could improve non-specific immunity of fish,antioxidant capacity,and two HSP70s mRNA expression levels,and enhance dis-ease resistance of fish against pathogenic infection.However,the combination of emodin and high-dose Vc showed no better effect,and the mechanism of their interaction needs further study.