Preliminary Study On The Toxic Effect Of Aflatoxin B₁ On Medaka Liver And The Effect Of Chitosan Oligosaccharide On Its Intervention And Mechanism

Aflatoxin B1（AFB₁）is a secondary metabolite of Aspergillus flavus and Aspergillus parasiticus,which is widely distributed in food crops and processed foods.The hazards associated with AFB₁ are mainly carcinogenicity,immunotoxicity,genotoxicity and hepatotoxicity.In mammals,acute and chronic liver injury caused by AFB₁ exposure has been theoretically established,but the mechanism of toxicity in aquatic models has been less studied.Chitosan oligosaccharide（COS）,a small molecular weight oligosaccharide with strong bioactivity and antioxidant capacity,is a possible drug for the treatment of AFB₁-induced liver injury.This thesis focuses on three aspects of the mechanism of aflatoxin B1-induced hepatotoxicity in the aquatic model medaka:first,acute liver injury in medaka from different doses of AFB₁exposure;second,intervention of COS in AFB₁-induced acute liver injury in medaka;and third,investigation of COS intervention in AFB₁-induced acute liver injury by RNA-Seq.The third part of the study investigated the effect of COS on AFB₁-induced acute liver injury in medaka by RNA-Seq.The methods and results of the experiments are as follows.（1）After 72 hours of single intraperitoneal injection of 0.25 g/L（LA group）and 1g/L（HA group）of AFB₁ in medaka,we analyzed AFB₁-induced liver injury in several phenotypic aspects,including survival and growth,body weight and liver weight index,liver histopathology,liver function injury indicators,changes in liver oxidative stress indicators,and principal component analysis of enzyme activity.As the concentration of AFB₁ increased,the degree of AFB₁-induced liver damage in the medaka increased,and the abnormal increase in enzyme activity tended to reduce the survival rate of the medaka,which suggests that AFB₁ has phenotypically caused toxic effects on the medaka that cannot be recovered in the short term.（2）To evaluate the effects of COS at different concentrations in medaka,a single intraperitoneal injection of 1 g/L of AFB₁ was administered,and 0.3%（LCOS group）and 0.6%（HCOS group）of COS was added to the diet before and after the injection,with a positive control group and 0.5%of silymarin（SIL）,a recognized hepatoprotective agent,added to the basal diet.The effects of COS intervention on AFB₁-induced liver injury in medaka were analyzed in terms of survival and growth,liver histopathology,liver function injury indicators,changes in liver oxidative stress indicators,and principal component analysis of enzyme activity,and were found to be progressively better with increasing COS concentrations,especially at high concentrations that differed from SIL.In particular,the effect of COS at high concentrations was comparable to that of SIL,and the intervention of COS inhibited the abnormal increase in enzyme activity,and the intervention of COS and SIL at high concentrations significantly reduced AFB₁-induced mortality in medaka.（3）A comparison of a single intraperitoneal injection of 1 g/L of AFB₁ and a 0.6%COS intervention in the basal diet of medaka was performed by RNA-Seq,and the effect of COS intervention on AFB₁-induced acute liver injury in medaka was initially explored at the genetic level.From the changes in the number of Differentially Expressed Genes（DEGs）compared to the CK group and the GO and KEGG enrichment analysis methods,it was found that COS intervention reduced AFB₁-induced liver genotoxicity in medaka to some extent and reduced or increased the abnormal expression of genes associated with liver disease.In summary,COS can interfere with AFB₁-induced acute liver injury in medaka.In this paper,the toxic effects of AFB₁ at different concentrations and the intervention effects of COS at different concentrations are explored,providing a preliminary exploration of the mechanisms of AFB₁-induced liver injury and the intervention mechanisms of COS,which could help develop natural active substances such as COS to provide a new cure for AFB₁-induced liver disease.